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	Index: head/cddl/contrib/opensolaris/cmd/zdb/zdb.c
	===================================================================
	--- head/cddl/contrib/opensolaris/cmd/zdb/zdb.c
	+++ head/cddl/contrib/opensolaris/cmd/zdb/zdb.c
	@@ -2281,14 +2281,14 @@
	object_count++;
	}

	- ASSERT3U(object_count, ==, usedobjs);
	-
	(void) printf("\n");

	if (error != ESRCH) {
	(void) fprintf(stderr, "dmu_object_next() = %d\n", error);
	abort();
	}
	+
	+ ASSERT3U(object_count, ==, usedobjs);
	}

	static void
	@@ -2788,6 +2788,7 @@

	mutex_enter(&spa->spa_scrub_lock);
	spa->spa_scrub_inflight--;
	+ spa->spa_load_verify_ios--;
	cv_broadcast(&spa->spa_scrub_io_cv);

	if (ioerr && !(zio->io_flags & ZIO_FLAG_SPECULATIVE)) {
	@@ -2859,9 +2860,10 @@
	flags \|= ZIO_FLAG_SPECULATIVE;

	mutex_enter(&spa->spa_scrub_lock);
	- while (spa->spa_scrub_inflight > max_inflight)
	+ while (spa->spa_load_verify_ios > max_inflight)
	cv_wait(&spa->spa_scrub_io_cv, &spa->spa_scrub_lock);
	spa->spa_scrub_inflight++;
	+ spa->spa_load_verify_ios++;
	mutex_exit(&spa->spa_scrub_lock);

	zio_nowait(zio_read(NULL, spa, bp, abd, size,
	Index: head/cddl/contrib/opensolaris/cmd/zpool/zpool_main.c
	===================================================================
	--- head/cddl/contrib/opensolaris/cmd/zpool/zpool_main.c
	+++ head/cddl/contrib/opensolaris/cmd/zpool/zpool_main.c
	@@ -1643,7 +1643,7 @@
	(void) nvlist_lookup_uint64_array(nv, ZPOOL_CONFIG_SCAN_STATS,
	(uint64_t **)&ps, &c);

	- if (ps && ps->pss_state == DSS_SCANNING &&
	+ if (ps != NULL && ps->pss_state == DSS_SCANNING &&
	vs->vs_scan_processed != 0 && children == 0) {
	(void) printf(gettext(" (%s)"),
	(ps->pss_func == POOL_SCAN_RESILVER) ?
	@@ -4254,11 +4254,13 @@
	print_scan_status(pool_scan_stat_t *ps)
	{
	time_t start, end, pause;
	- uint64_t elapsed, mins_left, hours_left;
	- uint64_t pass_exam, examined, total;
	- uint_t rate;
	+ uint64_t total_secs_left;
	+ uint64_t elapsed, secs_left, mins_left, hours_left, days_left;
	+ uint64_t pass_scanned, scanned, pass_issued, issued, total;
	+ uint_t scan_rate, issue_rate;
	double fraction_done;
	- char processed_buf[7], examined_buf[7], total_buf[7], rate_buf[7];
	+ char processed_buf[7], scanned_buf[7], issued_buf[7], total_buf[7];
	+ char srate_buf[7], irate_buf[7];

	(void) printf(gettext(" scan: "));

	@@ -4272,30 +4274,37 @@
	start = ps->pss_start_time;
	end = ps->pss_end_time;
	pause = ps->pss_pass_scrub_pause;
	+
	zfs_nicenum(ps->pss_processed, processed_buf, sizeof (processed_buf));

	assert(ps->pss_func == POOL_SCAN_SCRUB \|\|
	ps->pss_func == POOL_SCAN_RESILVER);
	- /*
	- * Scan is finished or canceled.
	- */
	- if (ps->pss_state == DSS_FINISHED) {
	- uint64_t minutes_taken = (end - start) / 60;
	- char *fmt = NULL;

	+ /* Scan is finished or canceled. */
	+ if (ps->pss_state == DSS_FINISHED) {
	+ total_secs_left = end - start;
	+ days_left = total_secs_left / 60 / 60 / 24;
	+ hours_left = (total_secs_left / 60 / 60) % 24;
	+ mins_left = (total_secs_left / 60) % 60;
	+ secs_left = (total_secs_left % 60);
	+
	if (ps->pss_func == POOL_SCAN_SCRUB) {
	- fmt = gettext("scrub repaired %s in %lluh%um with "
	- "%llu errors on %s");
	+ (void) printf(gettext("scrub repaired %s "
	+ "in %llu days %02llu:%02llu:%02llu "
	+ "with %llu errors on %s"), processed_buf,
	+ (u_longlong_t)days_left, (u_longlong_t)hours_left,
	+ (u_longlong_t)mins_left, (u_longlong_t)secs_left,
	+ (u_longlong_t)ps->pss_errors, ctime(&end));
	} else if (ps->pss_func == POOL_SCAN_RESILVER) {
	- fmt = gettext("resilvered %s in %lluh%um with "
	- "%llu errors on %s");
	+ (void) printf(gettext("resilvered %s "
	+ "in %llu days %02llu:%02llu:%02llu "
	+ "with %llu errors on %s"), processed_buf,
	+ (u_longlong_t)days_left, (u_longlong_t)hours_left,
	+ (u_longlong_t)mins_left, (u_longlong_t)secs_left,
	+ (u_longlong_t)ps->pss_errors, ctime(&end));
	+
	}
	- /* LINTED */
	- (void) printf(fmt, processed_buf,
	- (u_longlong_t)(minutes_taken / 60),
	- (uint_t)(minutes_taken % 60),
	- (u_longlong_t)ps->pss_errors,
	- ctime((time_t *)&end));
	+
	return;
	} else if (ps->pss_state == DSS_CANCELED) {
	if (ps->pss_func == POOL_SCAN_SCRUB) {
	@@ -4310,19 +4319,15 @@

	assert(ps->pss_state == DSS_SCANNING);

	- /*
	- * Scan is in progress.
	- */
	+ /* Scan is in progress. Resilvers can't be paused. */
	if (ps->pss_func == POOL_SCAN_SCRUB) {
	if (pause == 0) {
	(void) printf(gettext("scrub in progress since %s"),
	ctime(&start));
	} else {
	- char buf[32];
	- struct tm *p = localtime(&pause);
	- (void) strftime(buf, sizeof (buf), "%a %b %e %T %Y", p);
	- (void) printf(gettext("scrub paused since %s\n"), buf);
	- (void) printf(gettext("\tscrub started on %s"),
	+ (void) printf(gettext("scrub paused since %s"),
	+ ctime(&pause));
	+ (void) printf(gettext("\tscrub started on %s"),
	ctime(&start));
	}
	} else if (ps->pss_func == POOL_SCAN_RESILVER) {
	@@ -4330,49 +4335,67 @@
	ctime(&start));
	}

	- examined = ps->pss_examined ? ps->pss_examined : 1;
	+ scanned = ps->pss_examined;
	+ pass_scanned = ps->pss_pass_exam;
	+ issued = ps->pss_issued;
	+ pass_issued = ps->pss_pass_issued;
	total = ps->pss_to_examine;
	- fraction_done = (double)examined / total;

	- /* elapsed time for this pass */
	+ /* we are only done with a block once we have issued the IO for it */
	+ fraction_done = (double)issued / total;
	+
	+ /* elapsed time for this pass, rounding up to 1 if it's 0 */
	elapsed = time(NULL) - ps->pss_pass_start;
	elapsed -= ps->pss_pass_scrub_spent_paused;
	- elapsed = elapsed ? elapsed : 1;
	- pass_exam = ps->pss_pass_exam ? ps->pss_pass_exam : 1;
	- rate = pass_exam / elapsed;
	- rate = rate ? rate : 1;
	- mins_left = ((total - examined) / rate) / 60;
	- hours_left = mins_left / 60;
	+ elapsed = (elapsed != 0) ? elapsed : 1;

	- zfs_nicenum(examined, examined_buf, sizeof (examined_buf));
	+ scan_rate = pass_scanned / elapsed;
	+ issue_rate = pass_issued / elapsed;
	+ total_secs_left = (issue_rate != 0) ?
	+ ((total - issued) / issue_rate) : UINT64_MAX;
	+
	+ days_left = total_secs_left / 60 / 60 / 24;
	+ hours_left = (total_secs_left / 60 / 60) % 24;
	+ mins_left = (total_secs_left / 60) % 60;
	+ secs_left = (total_secs_left % 60);
	+
	+ /* format all of the numbers we will be reporting */
	+ zfs_nicenum(scanned, scanned_buf, sizeof (scanned_buf));
	+ zfs_nicenum(issued, issued_buf, sizeof (issued_buf));
	zfs_nicenum(total, total_buf, sizeof (total_buf));
	+ zfs_nicenum(scan_rate, srate_buf, sizeof (srate_buf));
	+ zfs_nicenum(issue_rate, irate_buf, sizeof (irate_buf));

	- /*
	- * do not print estimated time if hours_left is more than 30 days
	- * or we have a paused scrub
	- */
	+ /* doo not print estimated time if we have a paused scrub */
	if (pause == 0) {
	- zfs_nicenum(rate, rate_buf, sizeof (rate_buf));
	- (void) printf(gettext("\t%s scanned out of %s at %s/s"),
	- examined_buf, total_buf, rate_buf);
	- if (hours_left < (30 * 24)) {
	- (void) printf(gettext(", %lluh%um to go\n"),
	- (u_longlong_t)hours_left, (uint_t)(mins_left % 60));
	- } else {
	- (void) printf(gettext(
	- ", (scan is slow, no estimated time)\n"));
	- }
	+ (void) printf(gettext("\t%s scanned at %s/s, "
	+ "%s issued at %s/s, %s total\n"),
	+ scanned_buf, srate_buf, issued_buf, irate_buf, total_buf);
	} else {
	- (void) printf(gettext("\t%s scanned out of %s\n"),
	- examined_buf, total_buf);
	+ (void) printf(gettext("\t%s scanned, %s issued, %s total\n"),
	+ scanned_buf, issued_buf, total_buf);
	}

	if (ps->pss_func == POOL_SCAN_RESILVER) {
	- (void) printf(gettext(" %s resilvered, %.2f%% done\n"),
	+ (void) printf(gettext("\t%s resilvered, %.2f%% done"),
	processed_buf, 100 * fraction_done);
	} else if (ps->pss_func == POOL_SCAN_SCRUB) {
	- (void) printf(gettext(" %s repaired, %.2f%% done\n"),
	+ (void) printf(gettext("\t%s repaired, %.2f%% done"),
	processed_buf, 100 * fraction_done);
	+ }
	+
	+ if (pause == 0) {
	+ if (issue_rate >= 10 * 1024 * 1024) {
	+ (void) printf(gettext(", %llu days "
	+ "%02llu:%02llu:%02llu to go\n"),
	+ (u_longlong_t)days_left, (u_longlong_t)hours_left,
	+ (u_longlong_t)mins_left, (u_longlong_t)secs_left);
	+ } else {
	+ (void) printf(gettext(", no estimated "
	+ "completion time\n"));
	+ }
	+ } else {
	+ (void) printf(gettext("\n"));
	}
	}

	Index: head/cddl/contrib/opensolaris/cmd/ztest/ztest.c
	===================================================================
	--- head/cddl/contrib/opensolaris/cmd/ztest/ztest.c
	+++ head/cddl/contrib/opensolaris/cmd/ztest/ztest.c
	@@ -374,15 +374,15 @@
	{ ztest_fzap, 1, &zopt_sometimes },
	{ ztest_dmu_snapshot_create_destroy, 1, &zopt_sometimes },
	{ ztest_spa_create_destroy, 1, &zopt_sometimes },
	- { ztest_fault_inject, 1, &zopt_sometimes },
	+ { ztest_fault_inject, 1, &zopt_incessant },
	{ ztest_ddt_repair, 1, &zopt_sometimes },
	{ ztest_dmu_snapshot_hold, 1, &zopt_sometimes },
	{ ztest_reguid, 1, &zopt_rarely },
	{ ztest_spa_rename, 1, &zopt_rarely },
	- { ztest_scrub, 1, &zopt_rarely },
	+ { ztest_scrub, 1, &zopt_often },
	{ ztest_spa_upgrade, 1, &zopt_rarely },
	{ ztest_dsl_dataset_promote_busy, 1, &zopt_rarely },
	- { ztest_vdev_attach_detach, 1, &zopt_sometimes },
	+ { ztest_vdev_attach_detach, 1, &zopt_incessant },
	{ ztest_vdev_LUN_growth, 1, &zopt_rarely },
	{ ztest_vdev_add_remove, 1,
	&ztest_opts.zo_vdevtime },
	Index: head/cddl/contrib/opensolaris/lib/libzfs/common/libzfs_status.c
	===================================================================
	--- head/cddl/contrib/opensolaris/lib/libzfs/common/libzfs_status.c
	+++ head/cddl/contrib/opensolaris/lib/libzfs/common/libzfs_status.c
	@@ -219,7 +219,7 @@
	*/
	(void) nvlist_lookup_uint64_array(nvroot, ZPOOL_CONFIG_SCAN_STATS,
	(uint64_t **)&ps, &psc);
	- if (ps && ps->pss_func == POOL_SCAN_RESILVER &&
	+ if (ps != NULL && ps->pss_func == POOL_SCAN_RESILVER &&
	ps->pss_state == DSS_SCANNING)
	return (ZPOOL_STATUS_RESILVERING);

	Index: head/cddl/contrib/opensolaris/lib/libzpool/common/sys/zfs_context.h
	===================================================================
	--- head/cddl/contrib/opensolaris/lib/libzpool/common/sys/zfs_context.h
	+++ head/cddl/contrib/opensolaris/lib/libzpool/common/sys/zfs_context.h
	@@ -408,6 +408,7 @@
	#define TQ_NOQUEUE 0x02 /* Do not enqueue if can't dispatch */
	#define TQ_FRONT 0x08 /* Queue in front */

	+#define TASKQID_INVALID ((taskqid_t)0)

	extern taskq_t *system_taskq;

	@@ -421,6 +422,7 @@
	taskq_ent_t *);
	extern void taskq_destroy(taskq_t *);
	extern void taskq_wait(taskq_t *);
	+extern void taskq_wait_id(taskq_t *, taskqid_t);
	extern int taskq_member(taskq_t , void );
	extern void system_taskq_init(void);
	extern void system_taskq_fini(void);
	Index: head/cddl/contrib/opensolaris/lib/libzpool/common/taskq.c
	===================================================================
	--- head/cddl/contrib/opensolaris/lib/libzpool/common/taskq.c
	+++ head/cddl/contrib/opensolaris/lib/libzpool/common/taskq.c
	@@ -187,6 +187,12 @@
	mutex_exit(&tq->tq_lock);
	}

	+void
	+taskq_wait_id(taskq_t *tq, taskqid_t id)
	+{
	+ taskq_wait(tq);
	+}
	+
	static void *
	taskq_thread(void *arg)
	{
	Index: head/sys/cddl/compat/opensolaris/kern/opensolaris_taskq.c
	===================================================================
	--- head/sys/cddl/compat/opensolaris/kern/opensolaris_taskq.c
	+++ head/sys/cddl/compat/opensolaris/kern/opensolaris_taskq.c
	@@ -173,3 +173,9 @@
	{
	taskqueue_drain_all(tq->tq_queue);
	}
	+
	+void
	+taskq_wait_id(taskq_t *tq, taskqid_t id)
	+{
	+ taskq_wait(tq);
	+}
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
	@@ -339,7 +339,8 @@
	* minimum lifespan of a prefetch block in clock ticks
	* (initialized in arc_init())
	*/
	-static int arc_min_prefetch_lifespan;
	+static int zfs_arc_min_prefetch_ms = 1;
	+static int zfs_arc_min_prescient_prefetch_ms = 6;

	/*
	* If this percent of memory is free, don't throttle.
	@@ -779,8 +780,9 @@
	kstat_named_t arcstat_meta_limit;
	kstat_named_t arcstat_meta_max;
	kstat_named_t arcstat_meta_min;
	- kstat_named_t arcstat_sync_wait_for_async;
	+ kstat_named_t arcstat_async_upgrade_sync;
	kstat_named_t arcstat_demand_hit_predictive_prefetch;
	+ kstat_named_t arcstat_demand_hit_prescient_prefetch;
	} arc_stats_t;

	static arc_stats_t arc_stats = {
	@@ -877,8 +879,9 @@
	{ "arc_meta_limit", KSTAT_DATA_UINT64 },
	{ "arc_meta_max", KSTAT_DATA_UINT64 },
	{ "arc_meta_min", KSTAT_DATA_UINT64 },
	- { "sync_wait_for_async", KSTAT_DATA_UINT64 },
	+ { "async_upgrade_sync", KSTAT_DATA_UINT64 },
	{ "demand_hit_predictive_prefetch", KSTAT_DATA_UINT64 },
	+ { "demand_hit_prescient_prefetch", KSTAT_DATA_UINT64 },
	};

	#define ARCSTAT(stat) (arc_stats.stat.value.ui64)
	@@ -974,22 +977,23 @@

	struct arc_callback {
	void *acb_private;
	- arc_done_func_t *acb_done;
	+ arc_read_done_func_t *acb_done;
	arc_buf_t *acb_buf;
	boolean_t acb_compressed;
	zio_t *acb_zio_dummy;
	+ zio_t *acb_zio_head;
	arc_callback_t *acb_next;
	};

	typedef struct arc_write_callback arc_write_callback_t;

	struct arc_write_callback {
	- void *awcb_private;
	- arc_done_func_t *awcb_ready;
	- arc_done_func_t *awcb_children_ready;
	- arc_done_func_t *awcb_physdone;
	- arc_done_func_t *awcb_done;
	- arc_buf_t *awcb_buf;
	+ void *awcb_private;
	+ arc_write_done_func_t *awcb_ready;
	+ arc_write_done_func_t *awcb_children_ready;
	+ arc_write_done_func_t *awcb_physdone;
	+ arc_write_done_func_t *awcb_done;
	+ arc_buf_t *awcb_buf;
	};

	/*
	@@ -1229,6 +1233,8 @@
	#define HDR_IO_IN_PROGRESS(hdr) ((hdr)->b_flags & ARC_FLAG_IO_IN_PROGRESS)
	#define HDR_IO_ERROR(hdr) ((hdr)->b_flags & ARC_FLAG_IO_ERROR)
	#define HDR_PREFETCH(hdr) ((hdr)->b_flags & ARC_FLAG_PREFETCH)
	+#define HDR_PRESCIENT_PREFETCH(hdr) \
	+ ((hdr)->b_flags & ARC_FLAG_PRESCIENT_PREFETCH)
	#define HDR_COMPRESSION_ENABLED(hdr) \
	((hdr)->b_flags & ARC_FLAG_COMPRESSED_ARC)

	@@ -1392,6 +1398,11 @@
	SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, l2c_only_size, CTLFLAG_RD,
	&ARC_l2c_only.arcs_size.rc_count, 0, "size of mru state");

	+SYSCTL_UINT(_vfs_zfs, OID_AUTO, arc_min_prfetch_ms, CTLFLAG_RW,
	+ &zfs_arc_min_prefetch_ms, 0, "Min life of prefetch block in ms");
	+SYSCTL_UINT(_vfs_zfs, OID_AUTO, arc_min_prescient_prefetch_ms, CTLFLAG_RW,
	+ &zfs_arc_min_prescient_prefetch_ms, 0, "Min life oof prescient prefetched block in ms");
	+
	/*
	* L2ARC Internals
	*/
	@@ -3544,6 +3555,8 @@
	{
	arc_state_t evicted_state, state;
	int64_t bytes_evicted = 0;
	+ int min_lifetime = HDR_PRESCIENT_PREFETCH(hdr) ?
	+ zfs_arc_min_prescient_prefetch_ms : zfs_arc_min_prefetch_ms;

	ASSERT(MUTEX_HELD(hash_lock));
	ASSERT(HDR_HAS_L1HDR(hdr));
	@@ -3596,8 +3609,7 @@
	/* prefetch buffers have a minimum lifespan */
	if (HDR_IO_IN_PROGRESS(hdr) \|\|
	((hdr->b_flags & (ARC_FLAG_PREFETCH \| ARC_FLAG_INDIRECT)) &&
	- ddi_get_lbolt() - hdr->b_l1hdr.b_arc_access <
	- arc_min_prefetch_lifespan)) {
	+ ddi_get_lbolt() - hdr->b_l1hdr.b_arc_access < min_lifetime * hz)) {
	ARCSTAT_BUMP(arcstat_evict_skip);
	return (bytes_evicted);
	}
	@@ -4968,13 +4980,15 @@
	* - move the buffer to the head of the list if this is
	* another prefetch (to make it less likely to be evicted).
	*/
	- if (HDR_PREFETCH(hdr)) {
	+ if (HDR_PREFETCH(hdr) \|\| HDR_PRESCIENT_PREFETCH(hdr)) {
	if (refcount_count(&hdr->b_l1hdr.b_refcnt) == 0) {
	/* link protected by hash lock */
	ASSERT(multilist_link_active(
	&hdr->b_l1hdr.b_arc_node));
	} else {
	- arc_hdr_clear_flags(hdr, ARC_FLAG_PREFETCH);
	+ arc_hdr_clear_flags(hdr,
	+ ARC_FLAG_PREFETCH \|
	+ ARC_FLAG_PRESCIENT_PREFETCH);
	ARCSTAT_BUMP(arcstat_mru_hits);
	}
	hdr->b_l1hdr.b_arc_access = now;
	@@ -5005,10 +5019,13 @@
	* MFU state.
	*/

	- if (HDR_PREFETCH(hdr)) {
	+ if (HDR_PREFETCH(hdr) \|\| HDR_PRESCIENT_PREFETCH(hdr)) {
	new_state = arc_mru;
	- if (refcount_count(&hdr->b_l1hdr.b_refcnt) > 0)
	- arc_hdr_clear_flags(hdr, ARC_FLAG_PREFETCH);
	+ if (refcount_count(&hdr->b_l1hdr.b_refcnt) > 0) {
	+ arc_hdr_clear_flags(hdr,
	+ ARC_FLAG_PREFETCH \|
	+ ARC_FLAG_PRESCIENT_PREFETCH);
	+ }
	DTRACE_PROBE1(new_state__mru, arc_buf_hdr_t *, hdr);
	} else {
	new_state = arc_mfu;
	@@ -5029,11 +5046,7 @@
	* If it was a prefetch, we will explicitly move it to
	* the head of the list now.
	*/
	- if ((HDR_PREFETCH(hdr)) != 0) {
	- ASSERT(refcount_is_zero(&hdr->b_l1hdr.b_refcnt));
	- /* link protected by hash_lock */
	- ASSERT(multilist_link_active(&hdr->b_l1hdr.b_arc_node));
	- }
	+
	ARCSTAT_BUMP(arcstat_mfu_hits);
	hdr->b_l1hdr.b_arc_access = ddi_get_lbolt();
	} else if (hdr->b_l1hdr.b_state == arc_mfu_ghost) {
	@@ -5044,12 +5057,11 @@
	* MFU state.
	*/

	- if (HDR_PREFETCH(hdr)) {
	+ if (HDR_PREFETCH(hdr) \|\| HDR_PRESCIENT_PREFETCH(hdr)) {
	/*
	* This is a prefetch access...
	* move this block back to the MRU state.
	*/
	- ASSERT0(refcount_count(&hdr->b_l1hdr.b_refcnt));
	new_state = arc_mru;
	}

	@@ -5116,23 +5128,28 @@
	demand, prefetch, !HDR_ISTYPE_METADATA(hdr), data, metadata, hits);
	}

	-/* a generic arc_done_func_t which you can use */
	+/* a generic arc_read_done_func_t which you can use */
	/* ARGSUSED */
	void
	-arc_bcopy_func(zio_t zio, arc_buf_t buf, void *arg)
	+arc_bcopy_func(zio_t zio, const zbookmark_phys_t zb, const blkptr_t *bp,
	+ arc_buf_t buf, void arg)
	{
	- if (zio == NULL \|\| zio->io_error == 0)
	- bcopy(buf->b_data, arg, arc_buf_size(buf));
	+ if (buf == NULL)
	+ return;
	+
	+ bcopy(buf->b_data, arg, arc_buf_size(buf));
	arc_buf_destroy(buf, arg);
	}

	-/* a generic arc_done_func_t */
	+/* a generic arc_read_done_func_t */
	+/* ARGSUSED */
	void
	-arc_getbuf_func(zio_t zio, arc_buf_t buf, void *arg)
	+arc_getbuf_func(zio_t zio, const zbookmark_phys_t zb, const blkptr_t *bp,
	+ arc_buf_t buf, void arg)
	{
	arc_buf_t **bufp = arg;
	- if (zio && zio->io_error) {
	- arc_buf_destroy(buf, arg);
	+
	+ if (buf == NULL) {
	*bufp = NULL;
	} else {
	*bufp = buf;
	@@ -5164,7 +5181,6 @@
	arc_callback_t *callback_list;
	arc_callback_t *acb;
	boolean_t freeable = B_FALSE;
	- boolean_t no_zio_error = (zio->io_error == 0);

	/*
	* The hdr was inserted into hash-table and removed from lists
	@@ -5190,7 +5206,7 @@
	ASSERT3P(hash_lock, !=, NULL);
	}

	- if (no_zio_error) {
	+ if (zio->io_error == 0) {
	/* byteswap if necessary */
	if (BP_SHOULD_BYTESWAP(zio->io_bp)) {
	if (BP_GET_LEVEL(zio->io_bp) > 0) {
	@@ -5211,7 +5227,8 @@
	callback_list = hdr->b_l1hdr.b_acb;
	ASSERT3P(callback_list, !=, NULL);

	- if (hash_lock && no_zio_error && hdr->b_l1hdr.b_state == arc_anon) {
	+ if (hash_lock && zio->io_error == 0 &&
	+ hdr->b_l1hdr.b_state == arc_anon) {
	/*
	* Only call arc_access on anonymous buffers. This is because
	* if we've issued an I/O for an evicted buffer, we've already
	@@ -5232,14 +5249,21 @@
	if (!acb->acb_done)
	continue;

	- /* This is a demand read since prefetches don't use callbacks */
	callback_cnt++;

	+ if (zio->io_error != 0)
	+ continue;
	+
	int error = arc_buf_alloc_impl(hdr, acb->acb_private,
	- acb->acb_compressed, no_zio_error, &acb->acb_buf);
	- if (no_zio_error) {
	- zio->io_error = error;
	+ acb->acb_compressed,
	+ B_TRUE, &acb->acb_buf);
	+ if (error != 0) {
	+ arc_buf_destroy(acb->acb_buf, acb->acb_private);
	+ acb->acb_buf = NULL;
	}
	+
	+ if (zio->io_error == 0)
	+ zio->io_error = error;
	}
	hdr->b_l1hdr.b_acb = NULL;
	arc_hdr_clear_flags(hdr, ARC_FLAG_IO_IN_PROGRESS);
	@@ -5252,7 +5276,7 @@
	ASSERT(refcount_is_zero(&hdr->b_l1hdr.b_refcnt) \|\|
	callback_list != NULL);

	- if (no_zio_error) {
	+ if (zio->io_error == 0) {
	arc_hdr_verify(hdr, zio->io_bp);
	} else {
	arc_hdr_set_flags(hdr, ARC_FLAG_IO_ERROR);
	@@ -5285,8 +5309,10 @@

	/* execute each callback and free its structure */
	while ((acb = callback_list) != NULL) {
	- if (acb->acb_done)
	- acb->acb_done(zio, acb->acb_buf, acb->acb_private);
	+ if (acb->acb_done) {
	+ acb->acb_done(zio, &zio->io_bookmark, zio->io_bp,
	+ acb->acb_buf, acb->acb_private);
	+ }

	if (acb->acb_zio_dummy != NULL) {
	acb->acb_zio_dummy->io_error = zio->io_error;
	@@ -5320,7 +5346,7 @@
	* for readers of this block.
	*/
	int
	-arc_read(zio_t pio, spa_t spa, const blkptr_t bp, arc_done_func_t done,
	+arc_read(zio_t pio, spa_t spa, const blkptr_t bp, arc_read_done_func_t done,
	void *private, zio_priority_t priority, int zio_flags,
	arc_flags_t arc_flags, const zbookmark_phys_t zb)
	{
	@@ -5329,7 +5355,8 @@
	zio_t *rzio;
	uint64_t guid = spa_load_guid(spa);
	boolean_t compressed_read = (zio_flags & ZIO_FLAG_RAW) != 0;
	-
	+ int rc = 0;
	+
	ASSERT(!BP_IS_EMBEDDED(bp) \|\|
	BPE_GET_ETYPE(bp) == BP_EMBEDDED_TYPE_DATA);

	@@ -5347,32 +5374,20 @@
	*arc_flags \|= ARC_FLAG_CACHED;

	if (HDR_IO_IN_PROGRESS(hdr)) {
	+ zio_t *head_zio = hdr->b_l1hdr.b_acb->acb_zio_head;

	+ ASSERT3P(head_zio, !=, NULL);
	if ((hdr->b_flags & ARC_FLAG_PRIO_ASYNC_READ) &&
	priority == ZIO_PRIORITY_SYNC_READ) {
	/*
	- * This sync read must wait for an
	- * in-progress async read (e.g. a predictive
	- * prefetch). Async reads are queued
	- * separately at the vdev_queue layer, so
	- * this is a form of priority inversion.
	- * Ideally, we would "inherit" the demand
	- * i/o's priority by moving the i/o from
	- * the async queue to the synchronous queue,
	- * but there is currently no mechanism to do
	- * so. Track this so that we can evaluate
	- * the magnitude of this potential performance
	- * problem.
	- *
	- * Note that if the prefetch i/o is already
	- * active (has been issued to the device),
	- * the prefetch improved performance, because
	- * we issued it sooner than we would have
	- * without the prefetch.
	+ * This is a sync read that needs to wait for
	+ * an in-flight async read. Request that the
	+ * zio have its priority upgraded.
	*/
	- DTRACE_PROBE1(arc__sync__wait__for__async,
	+ zio_change_priority(head_zio, priority);
	+ DTRACE_PROBE1(arc__async__upgrade__sync,
	arc_buf_hdr_t *, hdr);
	- ARCSTAT_BUMP(arcstat_sync_wait_for_async);
	+ ARCSTAT_BUMP(arcstat_async_upgrade_sync);
	}
	if (hdr->b_flags & ARC_FLAG_PREDICTIVE_PREFETCH) {
	arc_hdr_clear_flags(hdr,
	@@ -5399,6 +5414,7 @@
	spa, NULL, NULL, NULL, zio_flags);

	ASSERT3P(acb->acb_done, !=, NULL);
	+ acb->acb_zio_head = head_zio;
	acb->acb_next = hdr->b_l1hdr.b_acb;
	hdr->b_l1hdr.b_acb = acb;
	mutex_exit(hash_lock);
	@@ -5426,17 +5442,32 @@
	arc_hdr_clear_flags(hdr,
	ARC_FLAG_PREDICTIVE_PREFETCH);
	}
	- ASSERT(!BP_IS_EMBEDDED(bp) \|\| !BP_IS_HOLE(bp));

	+ if (hdr->b_flags & ARC_FLAG_PRESCIENT_PREFETCH) {
	+ ARCSTAT_BUMP(
	+ arcstat_demand_hit_prescient_prefetch);
	+ arc_hdr_clear_flags(hdr,
	+ ARC_FLAG_PRESCIENT_PREFETCH);
	+ }
	+
	+ ASSERT(!BP_IS_EMBEDDED(bp) \|\| !BP_IS_HOLE(bp));
	/* Get a buf with the desired data in it. */
	- VERIFY0(arc_buf_alloc_impl(hdr, private,
	- compressed_read, B_TRUE, &buf));
	+ rc = arc_buf_alloc_impl(hdr, private,
	+ compressed_read, B_TRUE, &buf);
	+ if (rc != 0) {
	+ arc_buf_destroy(buf, private);
	+ buf = NULL;
	+ }
	+ ASSERT((zio_flags & ZIO_FLAG_SPECULATIVE) \|\|
	+ rc == 0 \|\| rc != ENOENT);
	} else if (*arc_flags & ARC_FLAG_PREFETCH &&
	refcount_count(&hdr->b_l1hdr.b_refcnt) == 0) {
	arc_hdr_set_flags(hdr, ARC_FLAG_PREFETCH);
	}
	DTRACE_PROBE1(arc__hit, arc_buf_hdr_t *, hdr);
	arc_access(hdr, hash_lock);
	+ if (*arc_flags & ARC_FLAG_PRESCIENT_PREFETCH)
	+ arc_hdr_set_flags(hdr, ARC_FLAG_PRESCIENT_PREFETCH);
	if (*arc_flags & ARC_FLAG_L2CACHE)
	arc_hdr_set_flags(hdr, ARC_FLAG_L2CACHE);
	mutex_exit(hash_lock);
	@@ -5446,7 +5477,7 @@
	data, metadata, hits);

	if (done)
	- done(NULL, buf, private);
	+ done(NULL, zb, bp, buf, private);
	} else {
	uint64_t lsize = BP_GET_LSIZE(bp);
	uint64_t psize = BP_GET_PSIZE(bp);
	@@ -5520,6 +5551,9 @@

	if (*arc_flags & ARC_FLAG_PREFETCH)
	arc_hdr_set_flags(hdr, ARC_FLAG_PREFETCH);
	+ if (*arc_flags & ARC_FLAG_PRESCIENT_PREFETCH)
	+ arc_hdr_set_flags(hdr, ARC_FLAG_PRESCIENT_PREFETCH);
	+
	if (*arc_flags & ARC_FLAG_L2CACHE)
	arc_hdr_set_flags(hdr, ARC_FLAG_L2CACHE);
	if (BP_GET_LEVEL(bp) > 0)
	@@ -5549,14 +5583,17 @@
	vd = NULL;
	}

	- if (priority == ZIO_PRIORITY_ASYNC_READ)
	+ /*
	+ * We count both async reads and scrub IOs as asynchronous so
	+ * that both can be upgraded in the event of a cache hit while
	+ * the read IO is still in-flight.
	+ */
	+ if (priority == ZIO_PRIORITY_ASYNC_READ \|\|
	+ priority == ZIO_PRIORITY_SCRUB)
	arc_hdr_set_flags(hdr, ARC_FLAG_PRIO_ASYNC_READ);
	else
	arc_hdr_clear_flags(hdr, ARC_FLAG_PRIO_ASYNC_READ);

	- if (hash_lock != NULL)
	- mutex_exit(hash_lock);
	-
	/*
	* At this point, we have a level 1 cache miss. Try again in
	* L2ARC if possible.
	@@ -5637,6 +5674,11 @@
	ZIO_FLAG_CANFAIL \|
	ZIO_FLAG_DONT_PROPAGATE \|
	ZIO_FLAG_DONT_RETRY, B_FALSE);
	+ acb->acb_zio_head = rzio;
	+
	+ if (hash_lock != NULL)
	+ mutex_exit(hash_lock);
	+
	DTRACE_PROBE2(l2arc__read, vdev_t *, vd,
	zio_t *, rzio);
	ARCSTAT_INCR(arcstat_l2_read_bytes, size);
	@@ -5651,6 +5693,8 @@
	return (0);

	/* l2arc read error; goto zio_read() */
	+ if (hash_lock != NULL)
	+ mutex_enter(hash_lock);
	} else {
	DTRACE_PROBE1(l2arc__miss,
	arc_buf_hdr_t *, hdr);
	@@ -5671,7 +5715,11 @@

	rzio = zio_read(pio, spa, bp, hdr->b_l1hdr.b_pabd, size,
	arc_read_done, hdr, priority, zio_flags, zb);
	+ acb->acb_zio_head = rzio;

	+ if (hash_lock != NULL)
	+ mutex_exit(hash_lock);
	+
	if (*arc_flags & ARC_FLAG_WAIT)
	return (zio_wait(rzio));

	@@ -6162,9 +6210,9 @@

	zio_t *
	arc_write(zio_t pio, spa_t spa, uint64_t txg, blkptr_t bp, arc_buf_t buf,
	- boolean_t l2arc, const zio_prop_t zp, arc_done_func_t ready,
	- arc_done_func_t children_ready, arc_done_func_t physdone,
	- arc_done_func_t done, void private, zio_priority_t priority,
	+ boolean_t l2arc, const zio_prop_t zp, arc_write_done_func_t ready,
	+ arc_write_done_func_t children_ready, arc_write_done_func_t physdone,
	+ arc_write_done_func_t done, void private, zio_priority_t priority,
	int zio_flags, const zbookmark_phys_t *zb)
	{
	arc_buf_hdr_t *hdr = buf->b_hdr;
	@@ -6590,9 +6638,6 @@

	mutex_init(&arc_dnlc_evicts_lock, NULL, MUTEX_DEFAULT, NULL);
	cv_init(&arc_dnlc_evicts_cv, NULL, CV_DEFAULT, NULL);
	-
	- /* Convert seconds to clock ticks */
	- arc_min_prefetch_lifespan = 1 * hz;

	/* set min cache to 1/32 of all memory, or arc_abs_min, whichever is more */
	arc_c_min = MAX(allmem / 32, arc_abs_min);
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c
	@@ -902,7 +902,8 @@
	}

	static void
	-dbuf_read_done(zio_t zio, arc_buf_t buf, void *vdb)
	+dbuf_read_done(zio_t zio, const zbookmark_phys_t zb, const blkptr_t *bp,
	+ arc_buf_t buf, void vdb)
	{
	dmu_buf_impl_t *db = vdb;

	@@ -916,19 +917,22 @@
	ASSERT(db->db.db_data == NULL);
	if (db->db_level == 0 && db->db_freed_in_flight) {
	/* we were freed in flight; disregard any error */
	+ if (buf == NULL) {
	+ buf = arc_alloc_buf(db->db_objset->os_spa,
	+ db, DBUF_GET_BUFC_TYPE(db), db->db.db_size);
	+ }
	arc_release(buf, db);
	bzero(buf->b_data, db->db.db_size);
	arc_buf_freeze(buf);
	db->db_freed_in_flight = FALSE;
	dbuf_set_data(db, buf);
	db->db_state = DB_CACHED;
	- } else if (zio == NULL \|\| zio->io_error == 0) {
	+ } else if (buf != NULL) {
	dbuf_set_data(db, buf);
	db->db_state = DB_CACHED;
	} else {
	ASSERT(db->db_blkid != DMU_BONUS_BLKID);
	ASSERT3P(db->db_buf, ==, NULL);
	- arc_buf_destroy(buf, db);
	db->db_state = DB_UNCACHED;
	}
	cv_broadcast(&db->db_changed);
	@@ -2326,7 +2330,8 @@
	* prefetch if the next block down is our target.
	*/
	static void
	-dbuf_prefetch_indirect_done(zio_t zio, arc_buf_t abuf, void *private)
	+dbuf_prefetch_indirect_done(zio_t zio, const zbookmark_phys_t zb,
	+ const blkptr_t iobp, arc_buf_t abuf, void *private)
	{
	dbuf_prefetch_arg_t *dpa = private;

	@@ -2365,13 +2370,18 @@
	dbuf_rele(db, FTAG);
	}

	+ if (abuf == NULL) {
	+ kmem_free(dpa, sizeof(*dpa));
	+ return;
	+ }
	+
	dpa->dpa_curlevel--;

	uint64_t nextblkid = dpa->dpa_zb.zb_blkid >>
	(dpa->dpa_epbs * (dpa->dpa_curlevel - dpa->dpa_zb.zb_level));
	blkptr_t bp = ((blkptr_t )abuf->b_data) +
	P2PHASE(nextblkid, 1ULL << dpa->dpa_epbs);
	- if (BP_IS_HOLE(bp) \|\| (zio != NULL && zio->io_error != 0)) {
	+ if (BP_IS_HOLE(bp)) {
	kmem_free(dpa, sizeof (*dpa));
	} else if (dpa->dpa_curlevel == dpa->dpa_zb.zb_level) {
	ASSERT3U(nextblkid, ==, dpa->dpa_zb.zb_blkid);
	@@ -3746,7 +3756,7 @@
	* ready callback so that we can properly handle an indirect
	* block that only contains holes.
	*/
	- arc_done_func_t *children_ready_cb = NULL;
	+ arc_write_done_func_t *children_ready_cb = NULL;
	if (db->db_level != 0)
	children_ready_cb = dbuf_write_children_ready;

	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/ddt.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/ddt.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/ddt.c
	@@ -1112,14 +1112,26 @@
	void
	ddt_sync(spa_t *spa, uint64_t txg)
	{
	+ dsl_scan_t *scn = spa->spa_dsl_pool->dp_scan;
	dmu_tx_t *tx;
	- zio_t *rio = zio_root(spa, NULL, NULL,
	- ZIO_FLAG_CANFAIL \| ZIO_FLAG_SPECULATIVE \| ZIO_FLAG_SELF_HEAL);
	+ zio_t *rio;

	ASSERT(spa_syncing_txg(spa) == txg);

	tx = dmu_tx_create_assigned(spa->spa_dsl_pool, txg);

	+ rio = zio_root(spa, NULL, NULL,
	+ ZIO_FLAG_CANFAIL \| ZIO_FLAG_SPECULATIVE \| ZIO_FLAG_SELF_HEAL);
	+
	+ /*
	+ * This function may cause an immediate scan of ddt blocks (see
	+ * the comment above dsl_scan_ddt() for details). We set the
	+ * scan's root zio here so that we can wait for any scan IOs in
	+ * addition to the regular ddt IOs.
	+ */
	+ ASSERT3P(scn->scn_zio_root, ==, NULL);
	+ scn->scn_zio_root = rio;
	+
	for (enum zio_checksum c = 0; c < ZIO_CHECKSUM_FUNCTIONS; c++) {
	ddt_t *ddt = spa->spa_ddt[c];
	if (ddt == NULL)
	@@ -1129,6 +1141,7 @@
	}

	(void) zio_wait(rio);
	+ scn->scn_zio_root = NULL;

	dmu_tx_commit(tx);
	}
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_objset.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_objset.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_objset.c
	@@ -349,6 +349,7 @@

	ASSERT(ds == NULL \|\| MUTEX_HELD(&ds->ds_opening_lock));

	+#if 0
	/*
	* The $ORIGIN dataset (if it exists) doesn't have an associated
	* objset, so there's no reason to open it. The $ORIGIN dataset
	@@ -359,6 +360,7 @@
	ASSERT3P(ds->ds_dir, !=,
	spa_get_dsl(spa)->dp_origin_snap->ds_dir);
	}
	+#endif

	os = kmem_zalloc(sizeof (objset_t), KM_SLEEP);
	os->os_dsl_dataset = ds;
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_traverse.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_traverse.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_traverse.c
	@@ -499,8 +499,9 @@
	const zbookmark_phys_t zb, const dnode_phys_t dnp, void *arg)
	{
	prefetch_data_t *pfd = arg;
	- arc_flags_t aflags = ARC_FLAG_NOWAIT \| ARC_FLAG_PREFETCH;
	-
	+ arc_flags_t aflags = ARC_FLAG_NOWAIT \| ARC_FLAG_PREFETCH \|
	+ ARC_FLAG_PRESCIENT_PREFETCH;
	+
	ASSERT(pfd->pd_bytes_fetched >= 0);
	if (bp == NULL)
	return (0);
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_scan.c
	@@ -51,28 +51,136 @@
	#include <sys/sa_impl.h>
	#include <sys/zfeature.h>
	#include <sys/abd.h>
	+#include <sys/range_tree.h>
	#ifdef _KERNEL
	#include <sys/zfs_vfsops.h>
	#endif

	+/*
	+ * Grand theory statement on scan queue sorting
	+ *
	+ * Scanning is implemented by recursively traversing all indirection levels
	+ * in an object and reading all blocks referenced from said objects. This
	+ * results in us approximately traversing the object from lowest logical
	+ * offset to the highest. For best performance, we would want the logical
	+ * blocks to be physically contiguous. However, this is frequently not the
	+ * case with pools given the allocation patterns of copy-on-write filesystems.
	+ * So instead, we put the I/Os into a reordering queue and issue them in a
	+ * way that will most benefit physical disks (LBA-order).
	+ *
	+ * Queue management:
	+ *
	+ * Ideally, we would want to scan all metadata and queue up all block I/O
	+ * prior to starting to issue it, because that allows us to do an optimal
	+ * sorting job. This can however consume large amounts of memory. Therefore
	+ * we continuously monitor the size of the queues and constrain them to 5%
	+ * (zfs_scan_mem_lim_fact) of physmem. If the queues grow larger than this
	+ * limit, we clear out a few of the largest extents at the head of the queues
	+ * to make room for more scanning. Hopefully, these extents will be fairly
	+ * large and contiguous, allowing us to approach sequential I/O throughput
	+ * even without a fully sorted tree.
	+ *
	+ * Metadata scanning takes place in dsl_scan_visit(), which is called from
	+ * dsl_scan_sync() every spa_sync(). If we have either fully scanned all
	+ * metadata on the pool, or we need to make room in memory because our
	+ * queues are too large, dsl_scan_visit() is postponed and
	+ * scan_io_queues_run() is called from dsl_scan_sync() instead. This implies
	+ * that metadata scanning and queued I/O issuing are mutually exclusive. This
	+ * allows us to provide maximum sequential I/O throughput for the majority of
	+ * I/O's issued since sequential I/O performance is significantly negatively
	+ * impacted if it is interleaved with random I/O.
	+ *
	+ * Implementation Notes
	+ *
	+ * One side effect of the queued scanning algorithm is that the scanning code
	+ * needs to be notified whenever a block is freed. This is needed to allow
	+ * the scanning code to remove these I/Os from the issuing queue. Additionally,
	+ * we do not attempt to queue gang blocks to be issued sequentially since this
	+ * is very hard to do and would have an extremely limitted performance benefit.
	+ * Instead, we simply issue gang I/Os as soon as we find them using the legacy
	+ * algorithm.
	+ *
	+ * Backwards compatibility
	+ *
	+ * This new algorithm is backwards compatible with the legacy on-disk data
	+ * structures (and therefore does not require a new feature flag).
	+ * Periodically during scanning (see zfs_scan_checkpoint_intval), the scan
	+ * will stop scanning metadata (in logical order) and wait for all outstanding
	+ * sorted I/O to complete. Once this is done, we write out a checkpoint
	+ * bookmark, indicating that we have scanned everything logically before it.
	+ * If the pool is imported on a machine without the new sorting algorithm,
	+ * the scan simply resumes from the last checkpoint using the legacy algorithm.
	+ */
	+
	typedef int (scan_cb_t)(dsl_pool_t , const blkptr_t ,
	const zbookmark_phys_t *);

	static scan_cb_t dsl_scan_scrub_cb;
	-static void dsl_scan_cancel_sync(void , dmu_tx_t );
	-static void dsl_scan_sync_state(dsl_scan_t , dmu_tx_t );
	-static boolean_t dsl_scan_restarting(dsl_scan_t , dmu_tx_t );

	-unsigned int zfs_top_maxinflight = 32; /* maximum I/Os per top-level */
	-unsigned int zfs_resilver_delay = 2; /* number of ticks to delay resilver */
	-unsigned int zfs_scrub_delay = 4; /* number of ticks to delay scrub */
	+static int scan_ds_queue_compare(const void a, const void b);
	+static int scan_prefetch_queue_compare(const void a, const void b);
	+static void scan_ds_queue_clear(dsl_scan_t *scn);
	+static boolean_t scan_ds_queue_contains(dsl_scan_t *scn, uint64_t dsobj,
	+ uint64_t *txg);
	+static void scan_ds_queue_insert(dsl_scan_t *scn, uint64_t dsobj, uint64_t txg);
	+static void scan_ds_queue_remove(dsl_scan_t *scn, uint64_t dsobj);
	+static void scan_ds_queue_sync(dsl_scan_t scn, dmu_tx_t tx);
	+
	+extern int zfs_vdev_async_write_active_min_dirty_percent;
	+
	+/*
	+ * By default zfs will check to ensure it is not over the hard memory
	+ * limit before each txg. If finer-grained control of this is needed
	+ * this value can be set to 1 to enable checking before scanning each
	+ * block.
	+ */
	+int zfs_scan_strict_mem_lim = B_FALSE;
	+
	+/*
	+ * Maximum number of parallelly executing I/Os per top-level vdev.
	+ * Tune with care. Very high settings (hundreds) are known to trigger
	+ * some firmware bugs and resets on certain SSDs.
	+ */
	+int zfs_top_maxinflight = 32; /* maximum I/Os per top-level */
	+unsigned int zfs_resilver_delay = 2; /* number of ticks to delay resilver -- 2 is a good number */
	+unsigned int zfs_scrub_delay = 4; /* number of ticks to delay scrub -- 4 is a good number */
	unsigned int zfs_scan_idle = 50; /* idle window in clock ticks */

	-unsigned int zfs_scan_min_time_ms = 1000; /* min millisecs to scrub per txg */
	+/*
	+ * Maximum number of parallelly executed bytes per leaf vdev. We attempt
	+ * to strike a balance here between keeping the vdev queues full of I/Os
	+ * at all times and not overflowing the queues to cause long latency,
	+ * which would cause long txg sync times. No matter what, we will not
	+ * overload the drives with I/O, since that is protected by
	+ * zfs_vdev_scrub_max_active.
	+ */
	+unsigned long zfs_scan_vdev_limit = 4 << 20;
	+
	+int zfs_scan_issue_strategy = 0;
	+int zfs_scan_legacy = B_FALSE; /* don't queue & sort zios, go direct */
	+uint64_t zfs_scan_max_ext_gap = 2 << 20; /* in bytes */
	+
	+unsigned int zfs_scan_checkpoint_intval = 7200; /* seconds */
	+#define ZFS_SCAN_CHECKPOINT_INTVAL SEC_TO_TICK(zfs_scan_checkpoint_intval)
	+
	+/*
	+ * fill_weight is non-tunable at runtime, so we copy it at module init from
	+ * zfs_scan_fill_weight. Runtime adjustments to zfs_scan_fill_weight would
	+ * break queue sorting.
	+ */
	+uint64_t zfs_scan_fill_weight = 3;
	+static uint64_t fill_weight;
	+
	+/* See dsl_scan_should_clear() for details on the memory limit tunables */
	+uint64_t zfs_scan_mem_lim_min = 16 << 20; /* bytes */
	+uint64_t zfs_scan_mem_lim_soft_max = 128 << 20; /* bytes */
	+int zfs_scan_mem_lim_fact = 20; /* fraction of physmem */
	+int zfs_scan_mem_lim_soft_fact = 20; /* fraction of mem lim above */
	+
	+unsigned int zfs_scrub_min_time_ms = 1000; /* min millisecs to scrub per txg */
	unsigned int zfs_free_min_time_ms = 1000; /* min millisecs to free per txg */
	unsigned int zfs_obsolete_min_time_ms = 500; /* min millisecs to obsolete per txg */
	-unsigned int zfs_resilver_min_time_ms = 3000; /* min millisecs to resilver
	- per txg */
	+unsigned int zfs_resilver_min_time_ms = 3000; /* min millisecs to resilver per txg */
	boolean_t zfs_no_scrub_io = B_FALSE; /* set to disable scrub i/o */
	boolean_t zfs_no_scrub_prefetch = B_FALSE; /* set to disable scrub prefetch */

	@@ -86,7 +194,7 @@
	SYSCTL_UINT(_vfs_zfs, OID_AUTO, scan_idle, CTLFLAG_RWTUN,
	&zfs_scan_idle, 0, "Idle scan window in clock ticks");
	SYSCTL_UINT(_vfs_zfs, OID_AUTO, scan_min_time_ms, CTLFLAG_RWTUN,
	- &zfs_scan_min_time_ms, 0, "Min millisecs to scrub per txg");
	+ &zfs_scrub_min_time_ms, 0, "Min millisecs to scrub per txg");
	SYSCTL_UINT(_vfs_zfs, OID_AUTO, free_min_time_ms, CTLFLAG_RWTUN,
	&zfs_free_min_time_ms, 0, "Min millisecs to free per txg");
	SYSCTL_UINT(_vfs_zfs, OID_AUTO, resilver_min_time_ms, CTLFLAG_RWTUN,
	@@ -95,6 +203,10 @@
	&zfs_no_scrub_io, 0, "Disable scrub I/O");
	SYSCTL_INT(_vfs_zfs, OID_AUTO, no_scrub_prefetch, CTLFLAG_RWTUN,
	&zfs_no_scrub_prefetch, 0, "Disable scrub prefetching");
	+SYSCTL_UINT(_vfs_zfs, OID_AUTO, zfs_scan_legacy, CTLFLAG_RWTUN,
	+ &zfs_scan_legacy, 0, "Scrub using legacy non-sequential method");
	+SYSCTL_UINT(_vfs_zfs, OID_AUTO, zfs_scan_checkpoint_interval, CTLFLAG_RWTUN,
	+ &zfs_scan_checkpoint_intval, 0, "Scan progress on-disk checkpointing interval");

	enum ddt_class zfs_scrub_ddt_class_max = DDT_CLASS_DUPLICATE;
	/* max number of blocks to free in a single TXG */
	@@ -102,7 +214,19 @@
	SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, free_max_blocks, CTLFLAG_RWTUN,
	&zfs_async_block_max_blocks, 0, "Maximum number of blocks to free in one TXG");

	+/*
	+ * We wait a few txgs after importing a pool to begin scanning so that
	+ * the import / mounting code isn't held up by scrub / resilver IO.
	+ * Unfortunately, it is a bit difficult to determine exactly how long
	+ * this will take since userspace will trigger fs mounts asynchronously
	+ * and the kernel will create zvol minors asynchronously. As a result,
	+ * the value provided here is a bit arbitrary, but represents a
	+ * reasonable estimate of how many txgs it will take to finish fully
	+ * importing a pool
	+ */
	+#define SCAN_IMPORT_WAIT_TXGS 5

	+
	#define DSL_SCAN_IS_SCRUB_RESILVER(scn) \
	((scn)->scn_phys.scn_func == POOL_SCAN_SCRUB \|\| \
	(scn)->scn_phys.scn_func == POOL_SCAN_RESILVER)
	@@ -124,6 +248,177 @@
	dsl_scan_scrub_cb, /* POOL_SCAN_RESILVER */
	};

	+/* In core node for the scn->scn_queue. Represents a dataset to be scanned */
	+typedef struct {
	+ uint64_t sds_dsobj;
	+ uint64_t sds_txg;
	+ avl_node_t sds_node;
	+} scan_ds_t;
	+
	+/*
	+ * This controls what conditions are placed on dsl_scan_sync_state():
	+ * SYNC_OPTIONAL) write out scn_phys iff scn_bytes_pending == 0
	+ * SYNC_MANDATORY) write out scn_phys always. scn_bytes_pending must be 0.
	+ * SYNC_CACHED) if scn_bytes_pending == 0, write out scn_phys. Otherwise
	+ * write out the scn_phys_cached version.
	+ * See dsl_scan_sync_state for details.
	+ */
	+typedef enum {
	+ SYNC_OPTIONAL,
	+ SYNC_MANDATORY,
	+ SYNC_CACHED
	+} state_sync_type_t;
	+
	+/*
	+ * This struct represents the minimum information needed to reconstruct a
	+ * zio for sequential scanning. This is useful because many of these will
	+ * accumulate in the sequential IO queues before being issued, so saving
	+ * memory matters here.
	+ */
	+typedef struct scan_io {
	+ /* fields from blkptr_t */
	+ uint64_t sio_offset;
	+ uint64_t sio_blk_prop;
	+ uint64_t sio_phys_birth;
	+ uint64_t sio_birth;
	+ zio_cksum_t sio_cksum;
	+ uint32_t sio_asize;
	+
	+ /* fields from zio_t */
	+ int sio_flags;
	+ zbookmark_phys_t sio_zb;
	+
	+ /* members for queue sorting */
	+ union {
	+ avl_node_t sio_addr_node; /* link into issueing queue */
	+ list_node_t sio_list_node; /* link for issuing to disk */
	+ } sio_nodes;
	+} scan_io_t;
	+
	+struct dsl_scan_io_queue {
	+ dsl_scan_t q_scn; / associated dsl_scan_t */
	+ vdev_t q_vd; / top-level vdev that this queue represents */
	+
	+ /* trees used for sorting I/Os and extents of I/Os */
	+ range_tree_t *q_exts_by_addr;
	+ avl_tree_t q_exts_by_size;
	+ avl_tree_t q_sios_by_addr;
	+
	+ /* members for zio rate limiting */
	+ uint64_t q_maxinflight_bytes;
	+ uint64_t q_inflight_bytes;
	+ kcondvar_t q_zio_cv; /* used under vd->vdev_scan_io_queue_lock */
	+
	+ /* per txg statistics */
	+ uint64_t q_total_seg_size_this_txg;
	+ uint64_t q_segs_this_txg;
	+ uint64_t q_total_zio_size_this_txg;
	+ uint64_t q_zios_this_txg;
	+};
	+
	+/* private data for dsl_scan_prefetch_cb() */
	+typedef struct scan_prefetch_ctx {
	+ refcount_t spc_refcnt; /* refcount for memory management */
	+ dsl_scan_t spc_scn; / dsl_scan_t for the pool */
	+ boolean_t spc_root; /* is this prefetch for an objset? */
	+ uint8_t spc_indblkshift; /* dn_indblkshift of current dnode */
	+ uint16_t spc_datablkszsec; /* dn_idatablkszsec of current dnode */
	+} scan_prefetch_ctx_t;
	+
	+/* private data for dsl_scan_prefetch() */
	+typedef struct scan_prefetch_issue_ctx {
	+ avl_node_t spic_avl_node; /* link into scn->scn_prefetch_queue */
	+ scan_prefetch_ctx_t spic_spc; / spc for the callback */
	+ blkptr_t spic_bp; /* bp to prefetch */
	+ zbookmark_phys_t spic_zb; /* bookmark to prefetch */
	+} scan_prefetch_issue_ctx_t;
	+
	+static void scan_exec_io(dsl_pool_t dp, const blkptr_t bp, int zio_flags,
	+ const zbookmark_phys_t zb, dsl_scan_io_queue_t queue);
	+static void scan_io_queue_insert_impl(dsl_scan_io_queue_t *queue,
	+ scan_io_t *sio);
	+
	+static dsl_scan_io_queue_t scan_io_queue_create(vdev_t vd);
	+static void scan_io_queues_destroy(dsl_scan_t *scn);
	+
	+static kmem_cache_t *sio_cache;
	+
	+void
	+scan_init(void)
	+{
	+ /*
	+ * This is used in ext_size_compare() to weight segments
	+ * based on how sparse they are. This cannot be changed
	+ * mid-scan and the tree comparison functions don't currently
	+ * have a mechansim for passing additional context to the
	+ * compare functions. Thus we store this value globally and
	+ * we only allow it to be set at module intiailization time
	+ */
	+ fill_weight = zfs_scan_fill_weight;
	+
	+ sio_cache = kmem_cache_create("sio_cache",
	+ sizeof (scan_io_t), 0, NULL, NULL, NULL, NULL, NULL, 0);
	+}
	+
	+void
	+scan_fini(void)
	+{
	+ kmem_cache_destroy(sio_cache);
	+}
	+
	+static inline boolean_t
	+dsl_scan_is_running(const dsl_scan_t *scn)
	+{
	+ return (scn->scn_phys.scn_state == DSS_SCANNING);
	+}
	+
	+boolean_t
	+dsl_scan_resilvering(dsl_pool_t *dp)
	+{
	+ return (dsl_scan_is_running(dp->dp_scan) &&
	+ dp->dp_scan->scn_phys.scn_func == POOL_SCAN_RESILVER);
	+}
	+
	+static inline void
	+sio2bp(const scan_io_t sio, blkptr_t bp, uint64_t vdev_id)
	+{
	+ bzero(bp, sizeof (*bp));
	+ DVA_SET_ASIZE(&bp->blk_dva[0], sio->sio_asize);
	+ DVA_SET_VDEV(&bp->blk_dva[0], vdev_id);
	+ DVA_SET_OFFSET(&bp->blk_dva[0], sio->sio_offset);
	+ bp->blk_prop = sio->sio_blk_prop;
	+ bp->blk_phys_birth = sio->sio_phys_birth;
	+ bp->blk_birth = sio->sio_birth;
	+ bp->blk_fill = 1; /* we always only work with data pointers */
	+ bp->blk_cksum = sio->sio_cksum;
	+}
	+
	+static inline void
	+bp2sio(const blkptr_t bp, scan_io_t sio, int dva_i)
	+{
	+ /* we discard the vdev id, since we can deduce it from the queue */
	+ sio->sio_offset = DVA_GET_OFFSET(&bp->blk_dva[dva_i]);
	+ sio->sio_asize = DVA_GET_ASIZE(&bp->blk_dva[dva_i]);
	+ sio->sio_blk_prop = bp->blk_prop;
	+ sio->sio_phys_birth = bp->blk_phys_birth;
	+ sio->sio_birth = bp->blk_birth;
	+ sio->sio_cksum = bp->blk_cksum;
	+}
	+
	+void
	+dsl_scan_global_init(void)
	+{
	+ /*
	+ * This is used in ext_size_compare() to weight segments
	+ * based on how sparse they are. This cannot be changed
	+ * mid-scan and the tree comparison functions don't currently
	+ * have a mechansim for passing additional context to the
	+ * compare functions. Thus we store this value globally and
	+ * we only allow it to be set at module intiailization time
	+ */
	+ fill_weight = zfs_scan_fill_weight;
	+}
	+
	int
	dsl_scan_init(dsl_pool_t *dp, uint64_t txg)
	{
	@@ -144,6 +439,13 @@
	scn->scn_async_destroying = spa_feature_is_active(dp->dp_spa,
	SPA_FEATURE_ASYNC_DESTROY);

	+ bcopy(&scn->scn_phys, &scn->scn_phys_cached, sizeof (scn->scn_phys));
	+ avl_create(&scn->scn_queue, scan_ds_queue_compare, sizeof (scan_ds_t),
	+ offsetof(scan_ds_t, sds_node));
	+ avl_create(&scn->scn_prefetch_queue, scan_prefetch_queue_compare,
	+ sizeof (scan_prefetch_issue_ctx_t),
	+ offsetof(scan_prefetch_issue_ctx_t, spic_avl_node));
	+
	err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
	"scrub_func", sizeof (uint64_t), 1, &f);
	if (err == 0) {
	@@ -154,7 +456,7 @@
	scn->scn_restart_txg = txg;
	zfs_dbgmsg("old-style scrub was in progress; "
	"restarting new-style scrub in txg %llu",
	- scn->scn_restart_txg);
	+ (longlong_t)scn->scn_restart_txg);

	/*
	* Load the queue obj from the old location so that it
	@@ -172,7 +474,14 @@
	else if (err)
	return (err);

	- if (scn->scn_phys.scn_state == DSS_SCANNING &&
	+ /*
	+ * We might be restarting after a reboot, so jump the issued
	+ * counter to how far we've scanned. We know we're consistent
	+ * up to here.
	+ */
	+ scn->scn_issued_before_pass = scn->scn_phys.scn_examined;
	+
	+ if (dsl_scan_is_running(scn) &&
	spa_prev_software_version(dp->dp_spa) < SPA_VERSION_SCAN) {
	/*
	* A new-type scrub was in progress on an old
	@@ -184,10 +493,26 @@
	scn->scn_restart_txg = txg;
	zfs_dbgmsg("new-style scrub was modified "
	"by old software; restarting in txg %llu",
	- scn->scn_restart_txg);
	+ (longlong_t)scn->scn_restart_txg);
	}
	}

	+ /* reload the queue into the in-core state */
	+ if (scn->scn_phys.scn_queue_obj != 0) {
	+ zap_cursor_t zc;
	+ zap_attribute_t za;
	+
	+ for (zap_cursor_init(&zc, dp->dp_meta_objset,
	+ scn->scn_phys.scn_queue_obj);
	+ zap_cursor_retrieve(&zc, &za) == 0;
	+ (void) zap_cursor_advance(&zc)) {
	+ scan_ds_queue_insert(scn,
	+ zfs_strtonum(za.za_name, NULL),
	+ za.za_first_integer);
	+ }
	+ zap_cursor_fini(&zc);
	+ }
	+
	spa_scan_stat_init(spa);
	return (0);
	}
	@@ -195,19 +520,116 @@
	void
	dsl_scan_fini(dsl_pool_t *dp)
	{
	- if (dp->dp_scan) {
	+ if (dp->dp_scan != NULL) {
	+ dsl_scan_t *scn = dp->dp_scan;
	+
	+ if (scn->scn_taskq != NULL)
	+ taskq_destroy(scn->scn_taskq);
	+ scan_ds_queue_clear(scn);
	+ avl_destroy(&scn->scn_queue);
	+ avl_destroy(&scn->scn_prefetch_queue);
	+
	kmem_free(dp->dp_scan, sizeof (dsl_scan_t));
	dp->dp_scan = NULL;
	}
	}

	+static boolean_t
	+dsl_scan_restarting(dsl_scan_t scn, dmu_tx_t tx)
	+{
	+ return (scn->scn_restart_txg != 0 &&
	+ scn->scn_restart_txg <= tx->tx_txg);
	+}
	+
	+boolean_t
	+dsl_scan_scrubbing(const dsl_pool_t *dp)
	+{
	+ dsl_scan_phys_t *scn_phys = &dp->dp_scan->scn_phys;
	+
	+ return (scn_phys->scn_state == DSS_SCANNING &&
	+ scn_phys->scn_func == POOL_SCAN_SCRUB);
	+}
	+
	+boolean_t
	+dsl_scan_is_paused_scrub(const dsl_scan_t *scn)
	+{
	+ return (dsl_scan_scrubbing(scn->scn_dp) &&
	+ scn->scn_phys.scn_flags & DSF_SCRUB_PAUSED);
	+}
	+
	+/*
	+ * Writes out a persistent dsl_scan_phys_t record to the pool directory.
	+ * Because we can be running in the block sorting algorithm, we do not always
	+ * want to write out the record, only when it is "safe" to do so. This safety
	+ * condition is achieved by making sure that the sorting queues are empty
	+ * (scn_bytes_pending == 0). When this condition is not true, the sync'd state
	+ * is inconsistent with how much actual scanning progress has been made. The
	+ * kind of sync to be performed is specified by the sync_type argument. If the
	+ * sync is optional, we only sync if the queues are empty. If the sync is
	+ * mandatory, we do a hard ASSERT to make sure that the queues are empty. The
	+ * third possible state is a "cached" sync. This is done in response to:
	+ * 1) The dataset that was in the last sync'd dsl_scan_phys_t having been
	+ * destroyed, so we wouldn't be able to restart scanning from it.
	+ * 2) The snapshot that was in the last sync'd dsl_scan_phys_t having been
	+ * superseded by a newer snapshot.
	+ * 3) The dataset that was in the last sync'd dsl_scan_phys_t having been
	+ * swapped with its clone.
	+ * In all cases, a cached sync simply rewrites the last record we've written,
	+ * just slightly modified. For the modifications that are performed to the
	+ * last written dsl_scan_phys_t, see dsl_scan_ds_destroyed,
	+ * dsl_scan_ds_snapshotted and dsl_scan_ds_clone_swapped.
	+ */
	+static void
	+dsl_scan_sync_state(dsl_scan_t scn, dmu_tx_t tx, state_sync_type_t sync_type)
	+{
	+ int i;
	+ spa_t *spa = scn->scn_dp->dp_spa;
	+
	+ ASSERT(sync_type != SYNC_MANDATORY \|\| scn->scn_bytes_pending == 0);
	+ if (scn->scn_bytes_pending == 0) {
	+ for (i = 0; i < spa->spa_root_vdev->vdev_children; i++) {
	+ vdev_t *vd = spa->spa_root_vdev->vdev_child[i];
	+ dsl_scan_io_queue_t *q = vd->vdev_scan_io_queue;
	+
	+ if (q == NULL)
	+ continue;
	+
	+ mutex_enter(&vd->vdev_scan_io_queue_lock);
	+ ASSERT3P(avl_first(&q->q_sios_by_addr), ==, NULL);
	+ ASSERT3P(avl_first(&q->q_exts_by_size), ==, NULL);
	+ ASSERT3P(range_tree_first(q->q_exts_by_addr), ==, NULL);
	+ mutex_exit(&vd->vdev_scan_io_queue_lock);
	+ }
	+
	+ if (scn->scn_phys.scn_queue_obj != 0)
	+ scan_ds_queue_sync(scn, tx);
	+ VERIFY0(zap_update(scn->scn_dp->dp_meta_objset,
	+ DMU_POOL_DIRECTORY_OBJECT,
	+ DMU_POOL_SCAN, sizeof (uint64_t), SCAN_PHYS_NUMINTS,
	+ &scn->scn_phys, tx));
	+ bcopy(&scn->scn_phys, &scn->scn_phys_cached,
	+ sizeof (scn->scn_phys));
	+
	+ if (scn->scn_checkpointing)
	+ zfs_dbgmsg("finish scan checkpoint");
	+
	+ scn->scn_checkpointing = B_FALSE;
	+ scn->scn_last_checkpoint = ddi_get_lbolt();
	+ } else if (sync_type == SYNC_CACHED) {
	+ VERIFY0(zap_update(scn->scn_dp->dp_meta_objset,
	+ DMU_POOL_DIRECTORY_OBJECT,
	+ DMU_POOL_SCAN, sizeof (uint64_t), SCAN_PHYS_NUMINTS,
	+ &scn->scn_phys_cached, tx));
	+ }
	+}
	+
	/* ARGSUSED */
	static int
	dsl_scan_setup_check(void arg, dmu_tx_t tx)
	{
	dsl_scan_t *scn = dmu_tx_pool(tx)->dp_scan;

	- if (scn->scn_phys.scn_state == DSS_SCANNING)
	+ if (dsl_scan_is_running(scn))
	return (SET_ERROR(EBUSY));

	return (0);
	@@ -222,7 +644,7 @@
	dsl_pool_t *dp = scn->scn_dp;
	spa_t *spa = dp->dp_spa;

	- ASSERT(scn->scn_phys.scn_state != DSS_SCANNING);
	+ ASSERT(!dsl_scan_is_running(scn));
	ASSERT(funcp > POOL_SCAN_NONE && funcp < POOL_SCAN_FUNCS);
	bzero(&scn->scn_phys, sizeof (scn->scn_phys));
	scn->scn_phys.scn_func = *funcp;
	@@ -233,8 +655,11 @@
	scn->scn_phys.scn_start_time = gethrestime_sec();
	scn->scn_phys.scn_errors = 0;
	scn->scn_phys.scn_to_examine = spa->spa_root_vdev->vdev_stat.vs_alloc;
	+ scn->scn_issued_before_pass = 0;
	scn->scn_restart_txg = 0;
	scn->scn_done_txg = 0;
	+ scn->scn_last_checkpoint = 0;
	+ scn->scn_checkpointing = B_FALSE;
	spa_scan_stat_init(spa);

	if (DSL_SCAN_IS_SCRUB_RESILVER(scn)) {
	@@ -267,8 +692,10 @@
	if (dp->dp_blkstats == NULL) {
	dp->dp_blkstats =
	kmem_alloc(sizeof (zfs_all_blkstats_t), KM_SLEEP);
	+ mutex_init(&dp->dp_blkstats->zab_lock, NULL,
	+ MUTEX_DEFAULT, NULL);
	}
	- bzero(dp->dp_blkstats, sizeof (zfs_all_blkstats_t));
	+ bzero(&dp->dp_blkstats->zab_type, sizeof (dp->dp_blkstats->zab_type));

	if (spa_version(spa) < SPA_VERSION_DSL_SCRUB)
	ot = DMU_OT_ZAP_OTHER;
	@@ -276,13 +703,52 @@
	scn->scn_phys.scn_queue_obj = zap_create(dp->dp_meta_objset,
	ot ? ot : DMU_OT_SCAN_QUEUE, DMU_OT_NONE, 0, tx);

	- dsl_scan_sync_state(scn, tx);
	+ bcopy(&scn->scn_phys, &scn->scn_phys_cached, sizeof (scn->scn_phys));

	+ dsl_scan_sync_state(scn, tx, SYNC_MANDATORY);
	+
	spa_history_log_internal(spa, "scan setup", tx,
	"func=%u mintxg=%llu maxtxg=%llu",
	*funcp, scn->scn_phys.scn_min_txg, scn->scn_phys.scn_max_txg);
	}

	+/*
	+ * Called by the ZFS_IOC_POOL_SCAN ioctl to start a scrub or resilver.
	+ * Can also be called to resume a paused scrub.
	+ */
	+int
	+dsl_scan(dsl_pool_t *dp, pool_scan_func_t func)
	+{
	+ spa_t *spa = dp->dp_spa;
	+ dsl_scan_t *scn = dp->dp_scan;
	+
	+ /*
	+ * Purge all vdev caches and probe all devices. We do this here
	+ * rather than in sync context because this requires a writer lock
	+ * on the spa_config lock, which we can't do from sync context. The
	+ * spa_scrub_reopen flag indicates that vdev_open() should not
	+ * attempt to start another scrub.
	+ */
	+ spa_vdev_state_enter(spa, SCL_NONE);
	+ spa->spa_scrub_reopen = B_TRUE;
	+ vdev_reopen(spa->spa_root_vdev);
	+ spa->spa_scrub_reopen = B_FALSE;
	+ (void) spa_vdev_state_exit(spa, NULL, 0);
	+
	+ if (func == POOL_SCAN_SCRUB && dsl_scan_is_paused_scrub(scn)) {
	+ /* got scrub start cmd, resume paused scrub */
	+ int err = dsl_scrub_set_pause_resume(scn->scn_dp,
	+ POOL_SCRUB_NORMAL);
	+ if (err == 0)
	+ return (ECANCELED);
	+
	+ return (SET_ERROR(err));
	+ }
	+
	+ return (dsl_sync_task(spa_name(spa), dsl_scan_setup_check,
	+ dsl_scan_setup_sync, &func, 0, ZFS_SPACE_CHECK_NONE));
	+}
	+
	/* ARGSUSED */
	static void
	dsl_scan_done(dsl_scan_t scn, boolean_t complete, dmu_tx_t tx)
	@@ -310,10 +776,11 @@
	}

	if (scn->scn_phys.scn_queue_obj != 0) {
	- VERIFY(0 == dmu_object_free(dp->dp_meta_objset,
	+ VERIFY0(dmu_object_free(dp->dp_meta_objset,
	scn->scn_phys.scn_queue_obj, tx));
	scn->scn_phys.scn_queue_obj = 0;
	}
	+ scan_ds_queue_clear(scn);

	scn->scn_phys.scn_flags &= ~DSF_SCRUB_PAUSED;

	@@ -321,14 +788,23 @@
	* If we were "restarted" from a stopped state, don't bother
	* with anything else.
	*/
	- if (scn->scn_phys.scn_state != DSS_SCANNING)
	+ if (!dsl_scan_is_running(scn)) {
	+ ASSERT(!scn->scn_is_sorted);
	return;
	+ }

	- if (complete)
	- scn->scn_phys.scn_state = DSS_FINISHED;
	- else
	- scn->scn_phys.scn_state = DSS_CANCELED;
	+ if (scn->scn_is_sorted) {
	+ scan_io_queues_destroy(scn);
	+ scn->scn_is_sorted = B_FALSE;

	+ if (scn->scn_taskq != NULL) {
	+ taskq_destroy(scn->scn_taskq);
	+ scn->scn_taskq = NULL;
	+ }
	+ }
	+
	+ scn->scn_phys.scn_state = complete ? DSS_FINISHED : DSS_CANCELED;
	+
	if (dsl_scan_restarting(scn, tx))
	spa_history_log_internal(spa, "scan aborted, restarting", tx,
	"errors=%llu", spa_get_errlog_size(spa));
	@@ -340,12 +816,6 @@
	"errors=%llu", spa_get_errlog_size(spa));

	if (DSL_SCAN_IS_SCRUB_RESILVER(scn)) {
	- mutex_enter(&spa->spa_scrub_lock);
	- while (spa->spa_scrub_inflight > 0) {
	- cv_wait(&spa->spa_scrub_io_cv,
	- &spa->spa_scrub_lock);
	- }
	- mutex_exit(&spa->spa_scrub_lock);
	spa->spa_scrub_started = B_FALSE;
	spa->spa_scrub_active = B_FALSE;

	@@ -381,6 +851,8 @@
	}

	scn->scn_phys.scn_end_time = gethrestime_sec();
	+
	+ ASSERT(!dsl_scan_is_running(scn));
	}

	/* ARGSUSED */
	@@ -389,7 +861,7 @@
	{
	dsl_scan_t *scn = dmu_tx_pool(tx)->dp_scan;

	- if (scn->scn_phys.scn_state != DSS_SCANNING)
	+ if (!dsl_scan_is_running(scn))
	return (SET_ERROR(ENOENT));
	return (0);
	}
	@@ -401,7 +873,7 @@
	dsl_scan_t *scn = dmu_tx_pool(tx)->dp_scan;

	dsl_scan_done(scn, B_FALSE, tx);
	- dsl_scan_sync_state(scn, tx);
	+ dsl_scan_sync_state(scn, tx, SYNC_MANDATORY);
	spa_event_notify(scn->scn_dp->dp_spa, NULL, NULL, ESC_ZFS_SCRUB_ABORT);
	}

	@@ -412,16 +884,6 @@
	dsl_scan_cancel_sync, NULL, 3, ZFS_SPACE_CHECK_RESERVED));
	}

	-boolean_t
	-dsl_scan_is_paused_scrub(const dsl_scan_t *scn)
	-{
	- if (dsl_scan_scrubbing(scn->scn_dp) &&
	- scn->scn_phys.scn_flags & DSF_SCRUB_PAUSED)
	- return (B_TRUE);
	-
	- return (B_FALSE);
	-}
	-
	static int
	dsl_scrub_pause_resume_check(void arg, dmu_tx_t tx)
	{
	@@ -456,7 +918,7 @@
	/* can't pause a scrub when there is no in-progress scrub */
	spa->spa_scan_pass_scrub_pause = gethrestime_sec();
	scn->scn_phys.scn_flags \|= DSF_SCRUB_PAUSED;
	- dsl_scan_sync_state(scn, tx);
	+ dsl_scan_sync_state(scn, tx, SYNC_CACHED);
	spa_event_notify(spa, NULL, NULL, ESC_ZFS_SCRUB_PAUSED);
	} else {
	ASSERT3U(*cmd, ==, POOL_SCRUB_NORMAL);
	@@ -470,7 +932,7 @@
	gethrestime_sec() - spa->spa_scan_pass_scrub_pause;
	spa->spa_scan_pass_scrub_pause = 0;
	scn->scn_phys.scn_flags &= ~DSF_SCRUB_PAUSED;
	- dsl_scan_sync_state(scn, tx);
	+ dsl_scan_sync_state(scn, tx, SYNC_CACHED);
	}
	}
	}
	@@ -486,25 +948,25 @@
	ZFS_SPACE_CHECK_RESERVED));
	}

	-boolean_t
	-dsl_scan_scrubbing(const dsl_pool_t *dp)
	+
	+/* start a new scan, or restart an existing one. */
	+void
	+dsl_resilver_restart(dsl_pool_t *dp, uint64_t txg)
	{
	- dsl_scan_t *scn = dp->dp_scan;
	+ if (txg == 0) {
	+ dmu_tx_t *tx;
	+ tx = dmu_tx_create_dd(dp->dp_mos_dir);
	+ VERIFY(0 == dmu_tx_assign(tx, TXG_WAIT));

	- if (scn->scn_phys.scn_state == DSS_SCANNING &&
	- scn->scn_phys.scn_func == POOL_SCAN_SCRUB)
	- return (B_TRUE);
	-
	- return (B_FALSE);
	+ txg = dmu_tx_get_txg(tx);
	+ dp->dp_scan->scn_restart_txg = txg;
	+ dmu_tx_commit(tx);
	+ } else {
	+ dp->dp_scan->scn_restart_txg = txg;
	+ }
	+ zfs_dbgmsg("restarting resilver txg=%llu", txg);
	}

	-static void dsl_scan_visitbp(blkptr_t bp, const zbookmark_phys_t zb,
	- dnode_phys_t dnp, dsl_dataset_t ds, dsl_scan_t *scn,
	- dmu_objset_type_t ostype, dmu_tx_t *tx);
	-static void dsl_scan_visitdnode(dsl_scan_t , dsl_dataset_t ds,
	- dmu_objset_type_t ostype,
	- dnode_phys_t dnp, uint64_t object, dmu_tx_t tx);
	-
	void
	dsl_free(dsl_pool_t dp, uint64_t txg, const blkptr_t bp)
	{
	@@ -519,27 +981,171 @@
	pio->io_flags));
	}

	-static uint64_t
	-dsl_scan_ds_maxtxg(dsl_dataset_t *ds)
	+static int
	+scan_ds_queue_compare(const void a, const void b)
	{
	- uint64_t smt = ds->ds_dir->dd_pool->dp_scan->scn_phys.scn_max_txg;
	- if (ds->ds_is_snapshot)
	- return (MIN(smt, dsl_dataset_phys(ds)->ds_creation_txg));
	- return (smt);
	+ const scan_ds_t sds_a = a, sds_b = b;
	+
	+ if (sds_a->sds_dsobj < sds_b->sds_dsobj)
	+ return (-1);
	+ if (sds_a->sds_dsobj == sds_b->sds_dsobj)
	+ return (0);
	+ return (1);
	}

	static void
	-dsl_scan_sync_state(dsl_scan_t scn, dmu_tx_t tx)
	+scan_ds_queue_clear(dsl_scan_t *scn)
	{
	- VERIFY0(zap_update(scn->scn_dp->dp_meta_objset,
	- DMU_POOL_DIRECTORY_OBJECT,
	- DMU_POOL_SCAN, sizeof (uint64_t), SCAN_PHYS_NUMINTS,
	- &scn->scn_phys, tx));
	+ void *cookie = NULL;
	+ scan_ds_t *sds;
	+ while ((sds = avl_destroy_nodes(&scn->scn_queue, &cookie)) != NULL) {
	+ kmem_free(sds, sizeof (*sds));
	+ }
	}

	-extern int zfs_vdev_async_write_active_min_dirty_percent;
	+static boolean_t
	+scan_ds_queue_contains(dsl_scan_t scn, uint64_t dsobj, uint64_t txg)
	+{
	+ scan_ds_t srch, *sds;

	+ srch.sds_dsobj = dsobj;
	+ sds = avl_find(&scn->scn_queue, &srch, NULL);
	+ if (sds != NULL && txg != NULL)
	+ *txg = sds->sds_txg;
	+ return (sds != NULL);
	+}
	+
	+static void
	+scan_ds_queue_insert(dsl_scan_t *scn, uint64_t dsobj, uint64_t txg)
	+{
	+ scan_ds_t *sds;
	+ avl_index_t where;
	+
	+ sds = kmem_zalloc(sizeof (*sds), KM_SLEEP);
	+ sds->sds_dsobj = dsobj;
	+ sds->sds_txg = txg;
	+
	+ VERIFY3P(avl_find(&scn->scn_queue, sds, &where), ==, NULL);
	+ avl_insert(&scn->scn_queue, sds, where);
	+}
	+
	+static void
	+scan_ds_queue_remove(dsl_scan_t *scn, uint64_t dsobj)
	+{
	+ scan_ds_t srch, *sds;
	+
	+ srch.sds_dsobj = dsobj;
	+
	+ sds = avl_find(&scn->scn_queue, &srch, NULL);
	+ VERIFY(sds != NULL);
	+ avl_remove(&scn->scn_queue, sds);
	+ kmem_free(sds, sizeof (*sds));
	+}
	+
	+static void
	+scan_ds_queue_sync(dsl_scan_t scn, dmu_tx_t tx)
	+{
	+ dsl_pool_t *dp = scn->scn_dp;
	+ spa_t *spa = dp->dp_spa;
	+ dmu_object_type_t ot = (spa_version(spa) >= SPA_VERSION_DSL_SCRUB) ?
	+ DMU_OT_SCAN_QUEUE : DMU_OT_ZAP_OTHER;
	+
	+ ASSERT0(scn->scn_bytes_pending);
	+ ASSERT(scn->scn_phys.scn_queue_obj != 0);
	+
	+ VERIFY0(dmu_object_free(dp->dp_meta_objset,
	+ scn->scn_phys.scn_queue_obj, tx));
	+ scn->scn_phys.scn_queue_obj = zap_create(dp->dp_meta_objset, ot,
	+ DMU_OT_NONE, 0, tx);
	+ for (scan_ds_t *sds = avl_first(&scn->scn_queue);
	+ sds != NULL; sds = AVL_NEXT(&scn->scn_queue, sds)) {
	+ VERIFY0(zap_add_int_key(dp->dp_meta_objset,
	+ scn->scn_phys.scn_queue_obj, sds->sds_dsobj,
	+ sds->sds_txg, tx));
	+ }
	+}
	+
	+/*
	+ * Computes the memory limit state that we're currently in. A sorted scan
	+ * needs quite a bit of memory to hold the sorting queue, so we need to
	+ * reasonably constrain the size so it doesn't impact overall system
	+ * performance. We compute two limits:
	+ * 1) Hard memory limit: if the amount of memory used by the sorting
	+ * queues on a pool gets above this value, we stop the metadata
	+ * scanning portion and start issuing the queued up and sorted
	+ * I/Os to reduce memory usage.
	+ * This limit is calculated as a fraction of physmem (by default 5%).
	+ * We constrain the lower bound of the hard limit to an absolute
	+ * minimum of zfs_scan_mem_lim_min (default: 16 MiB). We also constrain
	+ * the upper bound to 5% of the total pool size - no chance we'll
	+ * ever need that much memory, but just to keep the value in check.
	+ * 2) Soft memory limit: once we hit the hard memory limit, we start
	+ * issuing I/O to reduce queue memory usage, but we don't want to
	+ * completely empty out the queues, since we might be able to find I/Os
	+ * that will fill in the gaps of our non-sequential IOs at some point
	+ * in the future. So we stop the issuing of I/Os once the amount of
	+ * memory used drops below the soft limit (at which point we stop issuing
	+ * I/O and start scanning metadata again).
	+ *
	+ * This limit is calculated by subtracting a fraction of the hard
	+ * limit from the hard limit. By default this fraction is 5%, so
	+ * the soft limit is 95% of the hard limit. We cap the size of the
	+ * difference between the hard and soft limits at an absolute
	+ * maximum of zfs_scan_mem_lim_soft_max (default: 128 MiB) - this is
	+ * sufficient to not cause too frequent switching between the
	+ * metadata scan and I/O issue (even at 2k recordsize, 128 MiB's
	+ * worth of queues is about 1.2 GiB of on-pool data, so scanning
	+ * that should take at least a decent fraction of a second).
	+ */
	static boolean_t
	+dsl_scan_should_clear(dsl_scan_t *scn)
	+{
	+ vdev_t *rvd = scn->scn_dp->dp_spa->spa_root_vdev;
	+ uint64_t mlim_hard, mlim_soft, mused;
	+ uint64_t alloc = metaslab_class_get_alloc(spa_normal_class(
	+ scn->scn_dp->dp_spa));
	+
	+ mlim_hard = MAX((physmem / zfs_scan_mem_lim_fact) * PAGESIZE,
	+ zfs_scan_mem_lim_min);
	+ mlim_hard = MIN(mlim_hard, alloc / 20);
	+ mlim_soft = mlim_hard - MIN(mlim_hard / zfs_scan_mem_lim_soft_fact,
	+ zfs_scan_mem_lim_soft_max);
	+ mused = 0;
	+ for (uint64_t i = 0; i < rvd->vdev_children; i++) {
	+ vdev_t *tvd = rvd->vdev_child[i];
	+ dsl_scan_io_queue_t *queue;
	+
	+ mutex_enter(&tvd->vdev_scan_io_queue_lock);
	+ queue = tvd->vdev_scan_io_queue;
	+ if (queue != NULL) {
	+ /* #extents in exts_by_size = # in exts_by_addr */
	+ mused += avl_numnodes(&queue->q_exts_by_size) *
	+ sizeof (range_seg_t) +
	+ avl_numnodes(&queue->q_sios_by_addr) *
	+ sizeof (scan_io_t);
	+ }
	+ mutex_exit(&tvd->vdev_scan_io_queue_lock);
	+ }
	+
	+ dprintf("current scan memory usage: %llu bytes\n", (longlong_t)mused);
	+
	+ if (mused == 0)
	+ ASSERT0(scn->scn_bytes_pending);
	+
	+ /*
	+ * If we are above our hard limit, we need to clear out memory.
	+ * If we are below our soft limit, we need to accumulate sequential IOs.
	+ * Otherwise, we should keep doing whatever we are currently doing.
	+ */
	+ if (mused >= mlim_hard)
	+ return (B_TRUE);
	+ else if (mused < mlim_soft)
	+ return (B_FALSE);
	+ else
	+ return (scn->scn_clearing);
	+}
	+
	+static boolean_t
	dsl_scan_check_suspend(dsl_scan_t scn, const zbookmark_phys_t zb)
	{
	/* we never skip user/group accounting objects */
	@@ -558,9 +1164,6 @@

	/*
	* We suspend if:
	- * - we have scanned for the maximum time: an entire txg
	- * timeout (default 5 sec)
	- * or
	* - we have scanned for at least the minimum time (default 1 sec
	* for scrub, 3 sec for resilver), and either we have sufficient
	* dirty data that we are starting to write more quickly
	@@ -569,16 +1172,25 @@
	* or
	* - the spa is shutting down because this pool is being exported
	* or the machine is rebooting.
	+ * or
	+ * - the scan queue has reached its memory use limit
	*/
	- int mintime = (scn->scn_phys.scn_func == POOL_SCAN_RESILVER) ?
	- zfs_resilver_min_time_ms : zfs_scan_min_time_ms;
	- uint64_t elapsed_nanosecs = gethrtime() - scn->scn_sync_start_time;
	+ uint64_t elapsed_nanosecs = gethrtime();
	+ uint64_t curr_time_ns = gethrtime();
	+ uint64_t scan_time_ns = curr_time_ns - scn->scn_sync_start_time;
	+ uint64_t sync_time_ns = curr_time_ns -
	+ scn->scn_dp->dp_spa->spa_sync_starttime;
	+
	int dirty_pct = scn->scn_dp->dp_dirty_total * 100 / zfs_dirty_data_max;
	- if (elapsed_nanosecs / NANOSEC >= zfs_txg_timeout \|\|
	- (NSEC2MSEC(elapsed_nanosecs) > mintime &&
	- (txg_sync_waiting(scn->scn_dp) \|\|
	- dirty_pct >= zfs_vdev_async_write_active_min_dirty_percent)) \|\|
	- spa_shutting_down(scn->scn_dp->dp_spa)) {
	+ int mintime = (scn->scn_phys.scn_func == POOL_SCAN_RESILVER) ?
	+ zfs_resilver_min_time_ms : zfs_scrub_min_time_ms;
	+
	+ if ((NSEC2MSEC(scan_time_ns) > mintime &&
	+ (dirty_pct >= zfs_vdev_async_write_active_min_dirty_percent \|\|
	+ txg_sync_waiting(scn->scn_dp) \|\|
	+ NSEC2SEC(sync_time_ns) >= zfs_txg_timeout)) \|\|
	+ spa_shutting_down(scn->scn_dp->dp_spa) \|\|
	+ (zfs_scan_strict_mem_lim && dsl_scan_should_clear(scn))) {
	if (zb) {
	dprintf("suspending at bookmark %llx/%llx/%llx/%llx\n",
	(longlong_t)zb->zb_objset,
	@@ -586,12 +1198,16 @@
	(longlong_t)zb->zb_level,
	(longlong_t)zb->zb_blkid);
	scn->scn_phys.scn_bookmark = *zb;
	+ } else {
	+ dsl_scan_phys_t *scnp = &scn->scn_phys;
	+
	+ dprintf("suspending at at DDT bookmark "
	+ "%llx/%llx/%llx/%llx\n",
	+ (longlong_t)scnp->scn_ddt_bookmark.ddb_class,
	+ (longlong_t)scnp->scn_ddt_bookmark.ddb_type,
	+ (longlong_t)scnp->scn_ddt_bookmark.ddb_checksum,
	+ (longlong_t)scnp->scn_ddt_bookmark.ddb_cursor);
	}
	- dprintf("suspending at DDT bookmark %llx/%llx/%llx/%llx\n",
	- (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_class,
	- (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_type,
	- (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_checksum,
	- (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_cursor);
	scn->scn_suspending = B_TRUE;
	return (B_TRUE);
	}
	@@ -690,28 +1306,278 @@
	zil_free(zilog);
	}

	-/* ARGSUSED */
	+/*
	+ * We compare scan_prefetch_issue_ctx_t's based on their bookmarks. The idea
	+ * here is to sort the AVL tree by the order each block will be needed.
	+ */
	+static int
	+scan_prefetch_queue_compare(const void a, const void b)
	+{
	+ const scan_prefetch_issue_ctx_t spic_a = a, spic_b = b;
	+ const scan_prefetch_ctx_t *spc_a = spic_a->spic_spc;
	+ const scan_prefetch_ctx_t *spc_b = spic_b->spic_spc;
	+
	+ return (zbookmark_compare(spc_a->spc_datablkszsec,
	+ spc_a->spc_indblkshift, spc_b->spc_datablkszsec,
	+ spc_b->spc_indblkshift, &spic_a->spic_zb, &spic_b->spic_zb));
	+}
	+
	static void
	-dsl_scan_prefetch(dsl_scan_t scn, arc_buf_t buf, blkptr_t *bp,
	- uint64_t objset, uint64_t object, uint64_t blkid)
	+scan_prefetch_ctx_rele(scan_prefetch_ctx_t spc, void tag)
	{
	- zbookmark_phys_t czb;
	- arc_flags_t flags = ARC_FLAG_NOWAIT \| ARC_FLAG_PREFETCH;
	+ if (refcount_remove(&spc->spc_refcnt, tag) == 0) {
	+ refcount_destroy(&spc->spc_refcnt);
	+ kmem_free(spc, sizeof (scan_prefetch_ctx_t));
	+ }
	+}

	+static scan_prefetch_ctx_t *
	+scan_prefetch_ctx_create(dsl_scan_t scn, dnode_phys_t dnp, void *tag)
	+{
	+ scan_prefetch_ctx_t *spc;
	+
	+ spc = kmem_alloc(sizeof (scan_prefetch_ctx_t), KM_SLEEP);
	+ refcount_create(&spc->spc_refcnt);
	+ refcount_add(&spc->spc_refcnt, tag);
	+ spc->spc_scn = scn;
	+ if (dnp != NULL) {
	+ spc->spc_datablkszsec = dnp->dn_datablkszsec;
	+ spc->spc_indblkshift = dnp->dn_indblkshift;
	+ spc->spc_root = B_FALSE;
	+ } else {
	+ spc->spc_datablkszsec = 0;
	+ spc->spc_indblkshift = 0;
	+ spc->spc_root = B_TRUE;
	+ }
	+
	+ return (spc);
	+}
	+
	+static void
	+scan_prefetch_ctx_add_ref(scan_prefetch_ctx_t spc, void tag)
	+{
	+ refcount_add(&spc->spc_refcnt, tag);
	+}
	+
	+static boolean_t
	+dsl_scan_check_prefetch_resume(scan_prefetch_ctx_t *spc,
	+ const zbookmark_phys_t *zb)
	+{
	+ zbookmark_phys_t *last_zb = &spc->spc_scn->scn_prefetch_bookmark;
	+ dnode_phys_t tmp_dnp;
	+ dnode_phys_t *dnp = (spc->spc_root) ? NULL : &tmp_dnp;
	+
	+ if (zb->zb_objset != last_zb->zb_objset)
	+ return (B_TRUE);
	+ if ((int64_t)zb->zb_object < 0)
	+ return (B_FALSE);
	+
	+ tmp_dnp.dn_datablkszsec = spc->spc_datablkszsec;
	+ tmp_dnp.dn_indblkshift = spc->spc_indblkshift;
	+
	+ if (zbookmark_subtree_completed(dnp, zb, last_zb))
	+ return (B_TRUE);
	+
	+ return (B_FALSE);
	+}
	+
	+static void
	+dsl_scan_prefetch(scan_prefetch_ctx_t spc, blkptr_t bp, zbookmark_phys_t *zb)
	+{
	+ avl_index_t idx;
	+ dsl_scan_t *scn = spc->spc_scn;
	+ spa_t *spa = scn->scn_dp->dp_spa;
	+ scan_prefetch_issue_ctx_t *spic;
	+
	if (zfs_no_scrub_prefetch)
	return;

	- if (BP_IS_HOLE(bp) \|\| bp->blk_birth <= scn->scn_phys.scn_min_txg \|\|
	- (BP_GET_LEVEL(bp) == 0 && BP_GET_TYPE(bp) != DMU_OT_DNODE))
	+ if (BP_IS_HOLE(bp) \|\| bp->blk_birth <= scn->scn_phys.scn_cur_min_txg \|\|
	+ (BP_GET_LEVEL(bp) == 0 && BP_GET_TYPE(bp) != DMU_OT_DNODE &&
	+ BP_GET_TYPE(bp) != DMU_OT_OBJSET))
	return;

	- SET_BOOKMARK(&czb, objset, object, BP_GET_LEVEL(bp), blkid);
	+ if (dsl_scan_check_prefetch_resume(spc, zb))
	+ return;

	- (void) arc_read(scn->scn_zio_root, scn->scn_dp->dp_spa, bp,
	- NULL, NULL, ZIO_PRIORITY_ASYNC_READ,
	- ZIO_FLAG_CANFAIL \| ZIO_FLAG_SCAN_THREAD, &flags, &czb);
	+ scan_prefetch_ctx_add_ref(spc, scn);
	+ spic = kmem_alloc(sizeof (scan_prefetch_issue_ctx_t), KM_SLEEP);
	+ spic->spic_spc = spc;
	+ spic->spic_bp = *bp;
	+ spic->spic_zb = *zb;
	+
	+ /*
	+ * Add the IO to the queue of blocks to prefetch. This allows us to
	+ * prioritize blocks that we will need first for the main traversal
	+ * thread.
	+ */
	+ mutex_enter(&spa->spa_scrub_lock);
	+ if (avl_find(&scn->scn_prefetch_queue, spic, &idx) != NULL) {
	+ /* this block is already queued for prefetch */
	+ kmem_free(spic, sizeof (scan_prefetch_issue_ctx_t));
	+ scan_prefetch_ctx_rele(spc, scn);
	+ mutex_exit(&spa->spa_scrub_lock);
	+ return;
	+ }
	+
	+ avl_insert(&scn->scn_prefetch_queue, spic, idx);
	+ cv_broadcast(&spa->spa_scrub_io_cv);
	+ mutex_exit(&spa->spa_scrub_lock);
	}

	+static void
	+dsl_scan_prefetch_dnode(dsl_scan_t scn, dnode_phys_t dnp,
	+ uint64_t objset, uint64_t object)
	+{
	+ int i;
	+ zbookmark_phys_t zb;
	+ scan_prefetch_ctx_t *spc;
	+
	+ if (dnp->dn_nblkptr == 0 && !(dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR))
	+ return;
	+
	+ SET_BOOKMARK(&zb, objset, object, 0, 0);
	+
	+ spc = scan_prefetch_ctx_create(scn, dnp, FTAG);
	+
	+ for (i = 0; i < dnp->dn_nblkptr; i++) {
	+ zb.zb_level = BP_GET_LEVEL(&dnp->dn_blkptr[i]);
	+ zb.zb_blkid = i;
	+ dsl_scan_prefetch(spc, &dnp->dn_blkptr[i], &zb);
	+ }
	+
	+ if (dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) {
	+ zb.zb_level = 0;
	+ zb.zb_blkid = DMU_SPILL_BLKID;
	+ dsl_scan_prefetch(spc, &dnp->dn_spill, &zb);
	+ }
	+
	+ scan_prefetch_ctx_rele(spc, FTAG);
	+}
	+
	+void
	+dsl_scan_prefetch_cb(zio_t zio, const zbookmark_phys_t zb, const blkptr_t *bp,
	+ arc_buf_t buf, void private)
	+{
	+ scan_prefetch_ctx_t *spc = private;
	+ dsl_scan_t *scn = spc->spc_scn;
	+ spa_t *spa = scn->scn_dp->dp_spa;
	+
	+ /* broadcast that the IO has completed for rate limitting purposes */
	+ mutex_enter(&spa->spa_scrub_lock);
	+ ASSERT3U(spa->spa_scrub_inflight, >=, BP_GET_PSIZE(bp));
	+ spa->spa_scrub_inflight -= BP_GET_PSIZE(bp);
	+ cv_broadcast(&spa->spa_scrub_io_cv);
	+ mutex_exit(&spa->spa_scrub_lock);
	+
	+ /* if there was an error or we are done prefetching, just cleanup */
	+ if (buf == NULL \|\| scn->scn_suspending)
	+ goto out;
	+
	+ if (BP_GET_LEVEL(bp) > 0) {
	+ int i;
	+ blkptr_t *cbp;
	+ int epb = BP_GET_LSIZE(bp) >> SPA_BLKPTRSHIFT;
	+ zbookmark_phys_t czb;
	+
	+ for (i = 0, cbp = buf->b_data; i < epb; i++, cbp++) {
	+ SET_BOOKMARK(&czb, zb->zb_objset, zb->zb_object,
	+ zb->zb_level - 1, zb->zb_blkid * epb + i);
	+ dsl_scan_prefetch(spc, cbp, &czb);
	+ }
	+ } else if (BP_GET_TYPE(bp) == DMU_OT_DNODE) {
	+ dnode_phys_t *cdnp = buf->b_data;
	+ int i;
	+ int epb = BP_GET_LSIZE(bp) >> DNODE_SHIFT;
	+
	+ for (i = 0, cdnp = buf->b_data; i < epb; i++, cdnp++) {
	+ dsl_scan_prefetch_dnode(scn, cdnp,
	+ zb->zb_objset, zb->zb_blkid * epb + i);
	+ }
	+ } else if (BP_GET_TYPE(bp) == DMU_OT_OBJSET) {
	+ objset_phys_t *osp = buf->b_data;
	+
	+ dsl_scan_prefetch_dnode(scn, &osp->os_meta_dnode,
	+ zb->zb_objset, DMU_META_DNODE_OBJECT);
	+
	+ if (OBJSET_BUF_HAS_USERUSED(buf)) {
	+ dsl_scan_prefetch_dnode(scn,
	+ &osp->os_groupused_dnode, zb->zb_objset,
	+ DMU_GROUPUSED_OBJECT);
	+ dsl_scan_prefetch_dnode(scn,
	+ &osp->os_userused_dnode, zb->zb_objset,
	+ DMU_USERUSED_OBJECT);
	+ }
	+ }
	+
	+out:
	+ if (buf != NULL)
	+ arc_buf_destroy(buf, private);
	+ scan_prefetch_ctx_rele(spc, scn);
	+}
	+
	+/* ARGSUSED */
	+static void
	+dsl_scan_prefetch_thread(void *arg)
	+{
	+ dsl_scan_t *scn = arg;
	+ spa_t *spa = scn->scn_dp->dp_spa;
	+ vdev_t *rvd = spa->spa_root_vdev;
	+ uint64_t maxinflight = rvd->vdev_children * zfs_top_maxinflight;
	+ scan_prefetch_issue_ctx_t *spic;
	+
	+ /* loop until we are told to stop */
	+ while (!scn->scn_prefetch_stop) {
	+ arc_flags_t flags = ARC_FLAG_NOWAIT \|
	+ ARC_FLAG_PRESCIENT_PREFETCH \| ARC_FLAG_PREFETCH;
	+ int zio_flags = ZIO_FLAG_CANFAIL \| ZIO_FLAG_SCAN_THREAD;
	+
	+ mutex_enter(&spa->spa_scrub_lock);
	+
	+ /*
	+ * Wait until we have an IO to issue and are not above our
	+ * maximum in flight limit.
	+ */
	+ while (!scn->scn_prefetch_stop &&
	+ (avl_numnodes(&scn->scn_prefetch_queue) == 0 \|\|
	+ spa->spa_scrub_inflight >= scn->scn_maxinflight_bytes)) {
	+ cv_wait(&spa->spa_scrub_io_cv, &spa->spa_scrub_lock);
	+ }
	+
	+ /* recheck if we should stop since we waited for the cv */
	+ if (scn->scn_prefetch_stop) {
	+ mutex_exit(&spa->spa_scrub_lock);
	+ break;
	+ }
	+
	+ /* remove the prefetch IO from the tree */
	+ spic = avl_first(&scn->scn_prefetch_queue);
	+ spa->spa_scrub_inflight += BP_GET_PSIZE(&spic->spic_bp);
	+ avl_remove(&scn->scn_prefetch_queue, spic);
	+
	+ mutex_exit(&spa->spa_scrub_lock);
	+
	+ /* issue the prefetch asynchronously */
	+ (void) arc_read(scn->scn_zio_root, scn->scn_dp->dp_spa,
	+ &spic->spic_bp, dsl_scan_prefetch_cb, spic->spic_spc,
	+ ZIO_PRIORITY_SCRUB, zio_flags, &flags, &spic->spic_zb);
	+
	+ kmem_free(spic, sizeof (scan_prefetch_issue_ctx_t));
	+ }
	+
	+ ASSERT(scn->scn_prefetch_stop);
	+
	+ /* free any prefetches we didn't get to complete */
	+ mutex_enter(&spa->spa_scrub_lock);
	+ while ((spic = avl_first(&scn->scn_prefetch_queue)) != NULL) {
	+ avl_remove(&scn->scn_prefetch_queue, spic);
	+ scan_prefetch_ctx_rele(spic->spic_spc, scn);
	+ kmem_free(spic, sizeof (scan_prefetch_issue_ctx_t));
	+ }
	+ ASSERT0(avl_numnodes(&scn->scn_prefetch_queue));
	+ mutex_exit(&spa->spa_scrub_lock);
	+}
	+
	static boolean_t
	dsl_scan_check_resume(dsl_scan_t scn, const dnode_phys_t dnp,
	const zbookmark_phys_t *zb)
	@@ -748,6 +1614,13 @@
	return (B_FALSE);
	}

	+static void dsl_scan_visitbp(blkptr_t bp, const zbookmark_phys_t zb,
	+ dnode_phys_t dnp, dsl_dataset_t ds, dsl_scan_t *scn,
	+ dmu_objset_type_t ostype, dmu_tx_t *tx);
	+static void dsl_scan_visitdnode(
	+ dsl_scan_t , dsl_dataset_t ds, dmu_objset_type_t ostype,
	+ dnode_phys_t dnp, uint64_t object, dmu_tx_t tx);
	+
	/*
	* Return nonzero on i/o error.
	* Return new buf to write out in *bufp.
	@@ -769,16 +1642,12 @@
	arc_buf_t *buf;

	err = arc_read(NULL, dp->dp_spa, bp, arc_getbuf_func, &buf,
	- ZIO_PRIORITY_ASYNC_READ, zio_flags, &flags, zb);
	+ ZIO_PRIORITY_SCRUB, zio_flags, &flags, zb);
	if (err) {
	scn->scn_phys.scn_errors++;
	return (err);
	}
	for (i = 0, cbp = buf->b_data; i < epb; i++, cbp++) {
	- dsl_scan_prefetch(scn, buf, cbp, zb->zb_objset,
	- zb->zb_object, zb->zb_blkid * epb + i);
	- }
	- for (i = 0, cbp = buf->b_data; i < epb; i++, cbp++) {
	zbookmark_phys_t czb;

	SET_BOOKMARK(&czb, zb->zb_objset, zb->zb_object,
	@@ -791,24 +1660,17 @@
	} else if (BP_GET_TYPE(bp) == DMU_OT_DNODE) {
	arc_flags_t flags = ARC_FLAG_WAIT;
	dnode_phys_t *cdnp;
	- int i, j;
	+ int i;
	int epb = BP_GET_LSIZE(bp) >> DNODE_SHIFT;
	arc_buf_t *buf;

	err = arc_read(NULL, dp->dp_spa, bp, arc_getbuf_func, &buf,
	- ZIO_PRIORITY_ASYNC_READ, zio_flags, &flags, zb);
	+ ZIO_PRIORITY_SCRUB, zio_flags, &flags, zb);
	if (err) {
	scn->scn_phys.scn_errors++;
	return (err);
	}
	for (i = 0, cdnp = buf->b_data; i < epb; i++, cdnp++) {
	- for (j = 0; j < cdnp->dn_nblkptr; j++) {
	- blkptr_t *cbp = &cdnp->dn_blkptr[j];
	- dsl_scan_prefetch(scn, buf, cbp,
	- zb->zb_objset, zb->zb_blkid * epb + i, j);
	- }
	- }
	- for (i = 0, cdnp = buf->b_data; i < epb; i++, cdnp++) {
	dsl_scan_visitdnode(scn, ds, ostype,
	cdnp, zb->zb_blkid * epb + i, tx);
	}
	@@ -820,7 +1682,7 @@
	arc_buf_t *buf;

	err = arc_read(NULL, dp->dp_spa, bp, arc_getbuf_func, &buf,
	- ZIO_PRIORITY_ASYNC_READ, zio_flags, &flags, zb);
	+ ZIO_PRIORITY_SCRUB, zio_flags, &flags, zb);
	if (err) {
	scn->scn_phys.scn_errors++;
	return (err);
	@@ -886,20 +1748,14 @@
	dmu_objset_type_t ostype, dmu_tx_t *tx)
	{
	dsl_pool_t *dp = scn->scn_dp;
	- arc_buf_t *buf = NULL;
	- blkptr_t bp_toread = *bp;
	+ blkptr_t *bp_toread = NULL;

	- /* ASSERT(pbuf == NULL \|\| arc_released(pbuf)); */
	-
	if (dsl_scan_check_suspend(scn, zb))
	return;

	if (dsl_scan_check_resume(scn, dnp, zb))
	return;

	- if (BP_IS_HOLE(bp))
	- return;
	-
	scn->scn_visited_this_txg++;

	dprintf_bp(bp,
	@@ -908,12 +1764,22 @@
	zb->zb_objset, zb->zb_object, zb->zb_level, zb->zb_blkid,
	bp);

	- if (bp->blk_birth <= scn->scn_phys.scn_cur_min_txg)
	+ if (BP_IS_HOLE(bp)) {
	+ scn->scn_holes_this_txg++;
	return;
	+ }

	- if (dsl_scan_recurse(scn, ds, ostype, dnp, &bp_toread, zb, tx) != 0)
	+ if (bp->blk_birth <= scn->scn_phys.scn_cur_min_txg) {
	+ scn->scn_lt_min_this_txg++;
	return;
	+ }

	+ bp_toread = kmem_alloc(sizeof (blkptr_t), KM_SLEEP);
	+ bp_toread = bp;
	+
	+ if (dsl_scan_recurse(scn, ds, ostype, dnp, bp_toread, zb, tx) != 0)
	+ return;
	+
	/*
	* If dsl_scan_ddt() has already visited this block, it will have
	* already done any translations or scrubbing, so don't call the
	@@ -921,8 +1787,8 @@
	*/
	if (ddt_class_contains(dp->dp_spa,
	scn->scn_phys.scn_ddt_class_max, bp)) {
	- ASSERT(buf == NULL);
	- return;
	+ scn->scn_ddt_contained_this_txg++;
	+ goto out;
	}

	/*
	@@ -932,9 +1798,14 @@
	* Don't scan it now unless we need to because something
	* under it was modified.
	*/
	- if (BP_PHYSICAL_BIRTH(bp) <= scn->scn_phys.scn_cur_max_txg) {
	- scan_funcs[scn->scn_phys.scn_func](dp, bp, zb);
	+ if (BP_PHYSICAL_BIRTH(bp) > scn->scn_phys.scn_cur_max_txg) {
	+ scn->scn_gt_max_this_txg++;
	+ goto out;
	}
	+
	+ scan_funcs[scn->scn_phys.scn_func](dp, bp, zb);
	+out:
	+ kmem_free(bp_toread, sizeof (blkptr_t));
	}

	static void
	@@ -942,26 +1813,33 @@
	dmu_tx_t *tx)
	{
	zbookmark_phys_t zb;
	+ scan_prefetch_ctx_t *spc;

	SET_BOOKMARK(&zb, ds ? ds->ds_object : DMU_META_OBJSET,
	ZB_ROOT_OBJECT, ZB_ROOT_LEVEL, ZB_ROOT_BLKID);
	- dsl_scan_visitbp(bp, &zb, NULL,
	- ds, scn, DMU_OST_NONE, tx);

	+ if (ZB_IS_ZERO(&scn->scn_phys.scn_bookmark)) {
	+ SET_BOOKMARK(&scn->scn_prefetch_bookmark,
	+ zb.zb_objset, 0, 0, 0);
	+ } else {
	+ scn->scn_prefetch_bookmark = scn->scn_phys.scn_bookmark;
	+ }
	+
	+ scn->scn_objsets_visited_this_txg++;
	+
	+ spc = scan_prefetch_ctx_create(scn, NULL, FTAG);
	+ dsl_scan_prefetch(spc, bp, &zb);
	+ scan_prefetch_ctx_rele(spc, FTAG);
	+
	+ dsl_scan_visitbp(bp, &zb, NULL, ds, scn, DMU_OST_NONE, tx);
	+
	dprintf_ds(ds, "finished scan%s", "");
	}

	-void
	-dsl_scan_ds_destroyed(dsl_dataset_t ds, dmu_tx_t tx)
	+static void
	+ds_destroyed_scn_phys(dsl_dataset_t ds, dsl_scan_phys_t scn_phys)
	{
	- dsl_pool_t *dp = ds->ds_dir->dd_pool;
	- dsl_scan_t *scn = dp->dp_scan;
	- uint64_t mintxg;
	-
	- if (scn->scn_phys.scn_state != DSS_SCANNING)
	- return;
	-
	- if (scn->scn_phys.scn_bookmark.zb_objset == ds->ds_object) {
	+ if (scn_phys->scn_bookmark.zb_objset == ds->ds_object) {
	if (ds->ds_is_snapshot) {
	/*
	* Note:
	@@ -973,23 +1851,57 @@
	* ignore it when we retraverse it in
	* dsl_scan_visitds().
	*/
	- scn->scn_phys.scn_bookmark.zb_objset =
	+ scn_phys->scn_bookmark.zb_objset =
	dsl_dataset_phys(ds)->ds_next_snap_obj;
	zfs_dbgmsg("destroying ds %llu; currently traversing; "
	"reset zb_objset to %llu",
	(u_longlong_t)ds->ds_object,
	(u_longlong_t)dsl_dataset_phys(ds)->
	ds_next_snap_obj);
	- scn->scn_phys.scn_flags \|= DSF_VISIT_DS_AGAIN;
	+ scn_phys->scn_flags \|= DSF_VISIT_DS_AGAIN;
	} else {
	- SET_BOOKMARK(&scn->scn_phys.scn_bookmark,
	+ SET_BOOKMARK(&scn_phys->scn_bookmark,
	ZB_DESTROYED_OBJSET, 0, 0, 0);
	zfs_dbgmsg("destroying ds %llu; currently traversing; "
	"reset bookmark to -1,0,0,0",
	(u_longlong_t)ds->ds_object);
	}
	- } else if (zap_lookup_int_key(dp->dp_meta_objset,
	- scn->scn_phys.scn_queue_obj, ds->ds_object, &mintxg) == 0) {
	+ }
	+}
	+
	+/*
	+ * Invoked when a dataset is destroyed. We need to make sure that:
	+ *
	+ * 1) If it is the dataset that was currently being scanned, we write
	+ * a new dsl_scan_phys_t and marking the objset reference in it
	+ * as destroyed.
	+ * 2) Remove it from the work queue, if it was present.
	+ *
	+ * If the dataset was actually a snapshot, instead of marking the dataset
	+ * as destroyed, we instead substitute the next snapshot in line.
	+ */
	+void
	+dsl_scan_ds_destroyed(dsl_dataset_t ds, dmu_tx_t tx)
	+{
	+ dsl_pool_t *dp = ds->ds_dir->dd_pool;
	+ dsl_scan_t *scn = dp->dp_scan;
	+ uint64_t mintxg;
	+
	+ if (!dsl_scan_is_running(scn))
	+ return;
	+
	+ ds_destroyed_scn_phys(ds, &scn->scn_phys);
	+ ds_destroyed_scn_phys(ds, &scn->scn_phys_cached);
	+
	+ if (scan_ds_queue_contains(scn, ds->ds_object, &mintxg)) {
	+ scan_ds_queue_remove(scn, ds->ds_object);
	+ if (ds->ds_is_snapshot)
	+ scan_ds_queue_insert(scn,
	+ dsl_dataset_phys(ds)->ds_next_snap_obj, mintxg);
	+ }
	+
	+ if (zap_lookup_int_key(dp->dp_meta_objset, scn->scn_phys.scn_queue_obj,
	+ ds->ds_object, &mintxg) == 0) {
	ASSERT3U(dsl_dataset_phys(ds)->ds_num_children, <=, 1);
	VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
	scn->scn_phys.scn_queue_obj, ds->ds_object, tx));
	@@ -1018,9 +1930,28 @@
	* dsl_scan_sync() should be called after this, and should sync
	* out our changed state, but just to be safe, do it here.
	*/
	- dsl_scan_sync_state(scn, tx);
	+ dsl_scan_sync_state(scn, tx, SYNC_CACHED);
	}

	+static void
	+ds_snapshotted_bookmark(dsl_dataset_t ds, zbookmark_phys_t scn_bookmark)
	+{
	+ if (scn_bookmark->zb_objset == ds->ds_object) {
	+ scn_bookmark->zb_objset =
	+ dsl_dataset_phys(ds)->ds_prev_snap_obj;
	+ zfs_dbgmsg("snapshotting ds %llu; currently traversing; "
	+ "reset zb_objset to %llu",
	+ (u_longlong_t)ds->ds_object,
	+ (u_longlong_t)dsl_dataset_phys(ds)->ds_prev_snap_obj);
	+ }
	+}
	+
	+/*
	+ * Called when a dataset is snapshotted. If we were currently traversing
	+ * this snapshot, we reset our bookmark to point at the newly created
	+ * snapshot. We also modify our work queue to remove the old snapshot and
	+ * replace with the new one.
	+ */
	void
	dsl_scan_ds_snapshotted(dsl_dataset_t ds, dmu_tx_t tx)
	{
	@@ -1028,20 +1959,22 @@
	dsl_scan_t *scn = dp->dp_scan;
	uint64_t mintxg;

	- if (scn->scn_phys.scn_state != DSS_SCANNING)
	+ if (!dsl_scan_is_running(scn))
	return;

	ASSERT(dsl_dataset_phys(ds)->ds_prev_snap_obj != 0);

	- if (scn->scn_phys.scn_bookmark.zb_objset == ds->ds_object) {
	- scn->scn_phys.scn_bookmark.zb_objset =
	- dsl_dataset_phys(ds)->ds_prev_snap_obj;
	- zfs_dbgmsg("snapshotting ds %llu; currently traversing; "
	- "reset zb_objset to %llu",
	- (u_longlong_t)ds->ds_object,
	- (u_longlong_t)dsl_dataset_phys(ds)->ds_prev_snap_obj);
	- } else if (zap_lookup_int_key(dp->dp_meta_objset,
	- scn->scn_phys.scn_queue_obj, ds->ds_object, &mintxg) == 0) {
	+ ds_snapshotted_bookmark(ds, &scn->scn_phys.scn_bookmark);
	+ ds_snapshotted_bookmark(ds, &scn->scn_phys_cached.scn_bookmark);
	+
	+ if (scan_ds_queue_contains(scn, ds->ds_object, &mintxg)) {
	+ scan_ds_queue_remove(scn, ds->ds_object);
	+ scan_ds_queue_insert(scn,
	+ dsl_dataset_phys(ds)->ds_prev_snap_obj, mintxg);
	+ }
	+
	+ if (zap_lookup_int_key(dp->dp_meta_objset, scn->scn_phys.scn_queue_obj,
	+ ds->ds_object, &mintxg) == 0) {
	VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
	scn->scn_phys.scn_queue_obj, ds->ds_object, tx));
	VERIFY(zap_add_int_key(dp->dp_meta_objset,
	@@ -1052,37 +1985,59 @@
	(u_longlong_t)ds->ds_object,
	(u_longlong_t)dsl_dataset_phys(ds)->ds_prev_snap_obj);
	}
	- dsl_scan_sync_state(scn, tx);
	+
	+ dsl_scan_sync_state(scn, tx, SYNC_CACHED);
	}

	-void
	-dsl_scan_ds_clone_swapped(dsl_dataset_t ds1, dsl_dataset_t ds2, dmu_tx_t *tx)
	+static void
	+ds_clone_swapped_bookmark(dsl_dataset_t ds1, dsl_dataset_t ds2,
	+ zbookmark_phys_t *scn_bookmark)
	{
	- dsl_pool_t *dp = ds1->ds_dir->dd_pool;
	- dsl_scan_t *scn = dp->dp_scan;
	- uint64_t mintxg;
	-
	- if (scn->scn_phys.scn_state != DSS_SCANNING)
	- return;
	-
	- if (scn->scn_phys.scn_bookmark.zb_objset == ds1->ds_object) {
	- scn->scn_phys.scn_bookmark.zb_objset = ds2->ds_object;
	+ if (scn_bookmark->zb_objset == ds1->ds_object) {
	+ scn_bookmark->zb_objset = ds2->ds_object;
	zfs_dbgmsg("clone_swap ds %llu; currently traversing; "
	"reset zb_objset to %llu",
	(u_longlong_t)ds1->ds_object,
	(u_longlong_t)ds2->ds_object);
	- } else if (scn->scn_phys.scn_bookmark.zb_objset == ds2->ds_object) {
	- scn->scn_phys.scn_bookmark.zb_objset = ds1->ds_object;
	+ } else if (scn_bookmark->zb_objset == ds2->ds_object) {
	+ scn_bookmark->zb_objset = ds1->ds_object;
	zfs_dbgmsg("clone_swap ds %llu; currently traversing; "
	"reset zb_objset to %llu",
	(u_longlong_t)ds2->ds_object,
	(u_longlong_t)ds1->ds_object);
	}
	+}

	+/*
	+ * Called when a parent dataset and its clone are swapped. If we were
	+ * currently traversing the dataset, we need to switch to traversing the
	+ * newly promoted parent.
	+ */
	+void
	+dsl_scan_ds_clone_swapped(dsl_dataset_t ds1, dsl_dataset_t ds2, dmu_tx_t *tx)
	+{
	+ dsl_pool_t *dp = ds1->ds_dir->dd_pool;
	+ dsl_scan_t *scn = dp->dp_scan;
	+ uint64_t mintxg;
	+
	+ if (!dsl_scan_is_running(scn))
	+ return;
	+
	+ ds_clone_swapped_bookmark(ds1, ds2, &scn->scn_phys.scn_bookmark);
	+ ds_clone_swapped_bookmark(ds1, ds2, &scn->scn_phys_cached.scn_bookmark);
	+
	+ if (scan_ds_queue_contains(scn, ds1->ds_object, &mintxg)) {
	+ scan_ds_queue_remove(scn, ds1->ds_object);
	+ scan_ds_queue_insert(scn, ds2->ds_object, mintxg);
	+ }
	+ if (scan_ds_queue_contains(scn, ds2->ds_object, &mintxg)) {
	+ scan_ds_queue_remove(scn, ds2->ds_object);
	+ scan_ds_queue_insert(scn, ds1->ds_object, mintxg);
	+ }
	+
	if (zap_lookup_int_key(dp->dp_meta_objset, scn->scn_phys.scn_queue_obj,
	ds1->ds_object, &mintxg) == 0) {
	int err;
	-
	ASSERT3U(mintxg, ==, dsl_dataset_phys(ds1)->ds_prev_snap_txg);
	ASSERT3U(mintxg, ==, dsl_dataset_phys(ds2)->ds_prev_snap_txg);
	VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
	@@ -1100,8 +2055,9 @@
	"replacing with %llu",
	(u_longlong_t)ds1->ds_object,
	(u_longlong_t)ds2->ds_object);
	- } else if (zap_lookup_int_key(dp->dp_meta_objset,
	- scn->scn_phys.scn_queue_obj, ds2->ds_object, &mintxg) == 0) {
	+ }
	+ if (zap_lookup_int_key(dp->dp_meta_objset, scn->scn_phys.scn_queue_obj,
	+ ds2->ds_object, &mintxg) == 0) {
	ASSERT3U(mintxg, ==, dsl_dataset_phys(ds1)->ds_prev_snap_txg);
	ASSERT3U(mintxg, ==, dsl_dataset_phys(ds2)->ds_prev_snap_txg);
	VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
	@@ -1114,31 +2070,26 @@
	(u_longlong_t)ds1->ds_object);
	}

	- dsl_scan_sync_state(scn, tx);
	+ dsl_scan_sync_state(scn, tx, SYNC_CACHED);
	}

	-struct enqueue_clones_arg {
	- dmu_tx_t *tx;
	- uint64_t originobj;
	-};
	-
	/* ARGSUSED */
	static int
	enqueue_clones_cb(dsl_pool_t dp, dsl_dataset_t hds, void *arg)
	{
	- struct enqueue_clones_arg *eca = arg;
	+ uint64_t originobj = (uint64_t )arg;
	dsl_dataset_t *ds;
	int err;
	dsl_scan_t *scn = dp->dp_scan;

	- if (dsl_dir_phys(hds->ds_dir)->dd_origin_obj != eca->originobj)
	+ if (dsl_dir_phys(hds->ds_dir)->dd_origin_obj != originobj)
	return (0);

	err = dsl_dataset_hold_obj(dp, hds->ds_object, FTAG, &ds);
	if (err)
	return (err);

	- while (dsl_dataset_phys(ds)->ds_prev_snap_obj != eca->originobj) {
	+ while (dsl_dataset_phys(ds)->ds_prev_snap_obj != originobj) {
	dsl_dataset_t *prev;
	err = dsl_dataset_hold_obj(dp,
	dsl_dataset_phys(ds)->ds_prev_snap_obj, FTAG, &prev);
	@@ -1148,9 +2099,8 @@
	return (err);
	ds = prev;
	}
	- VERIFY(zap_add_int_key(dp->dp_meta_objset,
	- scn->scn_phys.scn_queue_obj, ds->ds_object,
	- dsl_dataset_phys(ds)->ds_prev_snap_txg, eca->tx) == 0);
	+ scan_ds_queue_insert(scn, ds->ds_object,
	+ dsl_dataset_phys(ds)->ds_prev_snap_txg);
	dsl_dataset_rele(ds, FTAG);
	return (0);
	}
	@@ -1160,6 +2110,7 @@
	{
	dsl_pool_t *dp = scn->scn_dp;
	dsl_dataset_t *ds;
	+ objset_t *os;

	VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));

	@@ -1195,14 +2146,17 @@
	dsl_dataset_name(ds, dsname);
	zfs_dbgmsg("scanning dataset %llu (%s) is unnecessary because "
	"cur_min_txg (%llu) >= max_txg (%llu)",
	- dsobj, dsname,
	- scn->scn_phys.scn_cur_min_txg,
	- scn->scn_phys.scn_max_txg);
	+ (longlong_t)dsobj, dsname,
	+ (longlong_t)scn->scn_phys.scn_cur_min_txg,
	+ (longlong_t)scn->scn_phys.scn_max_txg);
	kmem_free(dsname, MAXNAMELEN);

	goto out;
	}

	+ if (dmu_objset_from_ds(ds, &os))
	+ goto out;
	+
	/*
	* Only the ZIL in the head (non-snapshot) is valid. Even though
	* snapshots can have ZIL block pointers (which may be the same
	@@ -1212,14 +2166,8 @@
	* rather than in scan_recurse(), because the regular snapshot
	* block-sharing rules don't apply to it.
	*/
	- if (DSL_SCAN_IS_SCRUB_RESILVER(scn) && !dsl_dataset_is_snapshot(ds) &&
	- ds->ds_dir != dp->dp_origin_snap->ds_dir) {
	- objset_t *os;
	- if (dmu_objset_from_ds(ds, &os) != 0) {
	- goto out;
	- }
	+ if (!ds->ds_is_snapshot)
	dsl_scan_zil(dp, &os->os_zil_header);
	- }

	/*
	* Iterate over the bps in this ds.
	@@ -1252,9 +2200,8 @@
	if (scn->scn_phys.scn_flags & DSF_VISIT_DS_AGAIN) {
	zfs_dbgmsg("incomplete pass; visiting again");
	scn->scn_phys.scn_flags &= ~DSF_VISIT_DS_AGAIN;
	- VERIFY(zap_add_int_key(dp->dp_meta_objset,
	- scn->scn_phys.scn_queue_obj, ds->ds_object,
	- scn->scn_phys.scn_cur_max_txg, tx) == 0);
	+ scan_ds_queue_insert(scn, ds->ds_object,
	+ scn->scn_phys.scn_cur_max_txg);
	goto out;
	}

	@@ -1262,10 +2209,9 @@
	* Add descendent datasets to work queue.
	*/
	if (dsl_dataset_phys(ds)->ds_next_snap_obj != 0) {
	- VERIFY(zap_add_int_key(dp->dp_meta_objset,
	- scn->scn_phys.scn_queue_obj,
	+ scan_ds_queue_insert(scn,
	dsl_dataset_phys(ds)->ds_next_snap_obj,
	- dsl_dataset_phys(ds)->ds_creation_txg, tx) == 0);
	+ dsl_dataset_phys(ds)->ds_creation_txg);
	}
	if (dsl_dataset_phys(ds)->ds_num_children > 1) {
	boolean_t usenext = B_FALSE;
	@@ -1286,17 +2232,21 @@
	}

	if (usenext) {
	- VERIFY0(zap_join_key(dp->dp_meta_objset,
	- dsl_dataset_phys(ds)->ds_next_clones_obj,
	- scn->scn_phys.scn_queue_obj,
	- dsl_dataset_phys(ds)->ds_creation_txg, tx));
	+ zap_cursor_t zc;
	+ zap_attribute_t za;
	+ for (zap_cursor_init(&zc, dp->dp_meta_objset,
	+ dsl_dataset_phys(ds)->ds_next_clones_obj);
	+ zap_cursor_retrieve(&zc, &za) == 0;
	+ (void) zap_cursor_advance(&zc)) {
	+ scan_ds_queue_insert(scn,
	+ zfs_strtonum(za.za_name, NULL),
	+ dsl_dataset_phys(ds)->ds_creation_txg);
	+ }
	+ zap_cursor_fini(&zc);
	} else {
	- struct enqueue_clones_arg eca;
	- eca.tx = tx;
	- eca.originobj = ds->ds_object;
	-
	VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
	- enqueue_clones_cb, &eca, DS_FIND_CHILDREN));
	+ enqueue_clones_cb, &ds->ds_object,
	+ DS_FIND_CHILDREN));
	}
	}

	@@ -1308,7 +2258,6 @@
	static int
	enqueue_cb(dsl_pool_t dp, dsl_dataset_t hds, void *arg)
	{
	- dmu_tx_t *tx = arg;
	dsl_dataset_t *ds;
	int err;
	dsl_scan_t *scn = dp->dp_scan;
	@@ -1338,12 +2287,37 @@
	ds = prev;
	}

	- VERIFY(zap_add_int_key(dp->dp_meta_objset, scn->scn_phys.scn_queue_obj,
	- ds->ds_object, dsl_dataset_phys(ds)->ds_prev_snap_txg, tx) == 0);
	+ scan_ds_queue_insert(scn, ds->ds_object,
	+ dsl_dataset_phys(ds)->ds_prev_snap_txg);
	dsl_dataset_rele(ds, FTAG);
	return (0);
	}

	+/* ARGSUSED */
	+void
	+dsl_scan_ddt_entry(dsl_scan_t *scn, enum zio_checksum checksum,
	+ ddt_entry_t dde, dmu_tx_t tx)
	+{
	+ const ddt_key_t *ddk = &dde->dde_key;
	+ ddt_phys_t *ddp = dde->dde_phys;
	+ blkptr_t bp;
	+ zbookmark_phys_t zb = { 0 };
	+ int p;
	+
	+ if (scn->scn_phys.scn_state != DSS_SCANNING)
	+ return;
	+
	+ for (p = 0; p < DDT_PHYS_TYPES; p++, ddp++) {
	+ if (ddp->ddp_phys_birth == 0 \|\|
	+ ddp->ddp_phys_birth > scn->scn_phys.scn_max_txg)
	+ continue;
	+ ddt_bp_create(checksum, ddk, ddp, &bp);
	+
	+ scn->scn_visited_this_txg++;
	+ scan_funcs[scn->scn_phys.scn_func](scn->scn_dp, &bp, &zb);
	+ }
	+}
	+
	/*
	* Scrub/dedup interaction.
	*
	@@ -1416,36 +2390,20 @@
	ddb->ddb_class > scn->scn_phys.scn_ddt_class_max);
	}

	-/* ARGSUSED */
	-void
	-dsl_scan_ddt_entry(dsl_scan_t *scn, enum zio_checksum checksum,
	- ddt_entry_t dde, dmu_tx_t tx)
	+static uint64_t
	+dsl_scan_ds_maxtxg(dsl_dataset_t *ds)
	{
	- const ddt_key_t *ddk = &dde->dde_key;
	- ddt_phys_t *ddp = dde->dde_phys;
	- blkptr_t bp;
	- zbookmark_phys_t zb = { 0 };
	-
	- if (scn->scn_phys.scn_state != DSS_SCANNING)
	- return;
	-
	- for (int p = 0; p < DDT_PHYS_TYPES; p++, ddp++) {
	- if (ddp->ddp_phys_birth == 0 \|\|
	- ddp->ddp_phys_birth > scn->scn_phys.scn_max_txg)
	- continue;
	- ddt_bp_create(checksum, ddk, ddp, &bp);
	-
	- scn->scn_visited_this_txg++;
	- scan_funcs[scn->scn_phys.scn_func](scn->scn_dp, &bp, &zb);
	- }
	+ uint64_t smt = ds->ds_dir->dd_pool->dp_scan->scn_phys.scn_max_txg;
	+ if (ds->ds_is_snapshot)
	+ return (MIN(smt, dsl_dataset_phys(ds)->ds_creation_txg));
	+ return (smt);
	}

	static void
	dsl_scan_visit(dsl_scan_t scn, dmu_tx_t tx)
	{
	+ scan_ds_t *sds;
	dsl_pool_t *dp = scn->scn_dp;
	- zap_cursor_t zc;
	- zap_attribute_t za;

	if (scn->scn_phys.scn_ddt_bookmark.ddb_class <=
	scn->scn_phys.scn_ddt_class_max) {
	@@ -1469,7 +2427,7 @@

	if (spa_version(dp->dp_spa) < SPA_VERSION_DSL_SCRUB) {
	VERIFY0(dmu_objset_find_dp(dp, dp->dp_root_dir_obj,
	- enqueue_cb, tx, DS_FIND_CHILDREN));
	+ enqueue_cb, NULL, DS_FIND_CHILDREN));
	} else {
	dsl_scan_visitds(scn,
	dp->dp_origin_snap->ds_object, tx);
	@@ -1477,40 +2435,42 @@
	ASSERT(!scn->scn_suspending);
	} else if (scn->scn_phys.scn_bookmark.zb_objset !=
	ZB_DESTROYED_OBJSET) {
	+ uint64_t dsobj = scn->scn_phys.scn_bookmark.zb_objset;
	/*
	- * If we were suspended, continue from here. Note if the
	+ * If we were suspended, continue from here. Note if the
	* ds we were suspended on was deleted, the zb_objset may
	* be -1, so we will skip this and find a new objset
	* below.
	*/
	- dsl_scan_visitds(scn, scn->scn_phys.scn_bookmark.zb_objset, tx);
	+ dsl_scan_visitds(scn, dsobj, tx);
	if (scn->scn_suspending)
	return;
	}

	/*
	- * In case we were suspended right at the end of the ds, zero the
	+ * In case we suspended right at the end of the ds, zero the
	* bookmark so we don't think that we're still trying to resume.
	*/
	bzero(&scn->scn_phys.scn_bookmark, sizeof (zbookmark_phys_t));

	- /* keep pulling things out of the zap-object-as-queue */
	- while (zap_cursor_init(&zc, dp->dp_meta_objset,
	- scn->scn_phys.scn_queue_obj),
	- zap_cursor_retrieve(&zc, &za) == 0) {
	+ /*
	+ * Keep pulling things out of the dataset avl queue. Updates to the
	+ * persistent zap-object-as-queue happen only at checkpoints.
	+ */
	+ while ((sds = avl_first(&scn->scn_queue)) != NULL) {
	dsl_dataset_t *ds;
	- uint64_t dsobj;
	+ uint64_t dsobj = sds->sds_dsobj;
	+ uint64_t txg = sds->sds_txg;

	- dsobj = zfs_strtonum(za.za_name, NULL);
	- VERIFY3U(0, ==, zap_remove_int(dp->dp_meta_objset,
	- scn->scn_phys.scn_queue_obj, dsobj, tx));
	+ /* dequeue and free the ds from the queue */
	+ scan_ds_queue_remove(scn, dsobj);
	+ sds = NULL; /* must not be touched after removal */

	- /* Set up min/max txg */
	+ /* Set up min / max txg */
	VERIFY3U(0, ==, dsl_dataset_hold_obj(dp, dsobj, FTAG, &ds));
	- if (za.za_first_integer != 0) {
	+ if (txg != 0) {
	scn->scn_phys.scn_cur_min_txg =
	- MAX(scn->scn_phys.scn_min_txg,
	- za.za_first_integer);
	+ MAX(scn->scn_phys.scn_min_txg, txg);
	} else {
	scn->scn_phys.scn_cur_min_txg =
	MAX(scn->scn_phys.scn_min_txg,
	@@ -1520,14 +2480,367 @@
	dsl_dataset_rele(ds, FTAG);

	dsl_scan_visitds(scn, dsobj, tx);
	- zap_cursor_fini(&zc);
	if (scn->scn_suspending)
	return;
	}
	- zap_cursor_fini(&zc);
	+ /* No more objsets to fetch, we're done */
	+ scn->scn_phys.scn_bookmark.zb_objset = ZB_DESTROYED_OBJSET;
	+ ASSERT0(scn->scn_suspending);
	}

	+static uint64_t
	+dsl_scan_count_leaves(vdev_t *vd)
	+{
	+ uint64_t i, leaves = 0;
	+
	+ /* we only count leaves that belong to the main pool and are readable */
	+ if (vd->vdev_islog \|\| vd->vdev_isspare \|\|
	+ vd->vdev_isl2cache \|\| !vdev_readable(vd))
	+ return (0);
	+
	+ if (vd->vdev_ops->vdev_op_leaf)
	+ return (1);
	+
	+ for (i = 0; i < vd->vdev_children; i++) {
	+ leaves += dsl_scan_count_leaves(vd->vdev_child[i]);
	+ }
	+
	+ return (leaves);
	+}
	+
	+
	+static void
	+scan_io_queues_update_zio_stats(dsl_scan_io_queue_t q, const blkptr_t bp)
	+{
	+ int i;
	+ uint64_t cur_size = 0;
	+
	+ for (i = 0; i < BP_GET_NDVAS(bp); i++) {
	+ cur_size += DVA_GET_ASIZE(&bp->blk_dva[i]);
	+ }
	+
	+ q->q_total_zio_size_this_txg += cur_size;
	+ q->q_zios_this_txg++;
	+}
	+
	+static void
	+scan_io_queues_update_seg_stats(dsl_scan_io_queue_t *q, uint64_t start,
	+ uint64_t end)
	+{
	+ q->q_total_seg_size_this_txg += end - start;
	+ q->q_segs_this_txg++;
	+}
	+
	static boolean_t
	+scan_io_queue_check_suspend(dsl_scan_t *scn)
	+{
	+ /* See comment in dsl_scan_check_suspend() */
	+ uint64_t curr_time_ns = gethrtime();
	+ uint64_t scan_time_ns = curr_time_ns - scn->scn_sync_start_time;
	+ uint64_t sync_time_ns = curr_time_ns -
	+ scn->scn_dp->dp_spa->spa_sync_starttime;
	+ int dirty_pct = scn->scn_dp->dp_dirty_total * 100 / zfs_dirty_data_max;
	+ int mintime = (scn->scn_phys.scn_func == POOL_SCAN_RESILVER) ?
	+ zfs_resilver_min_time_ms : zfs_scrub_min_time_ms;
	+
	+ return ((NSEC2MSEC(scan_time_ns) > mintime &&
	+ (dirty_pct >= zfs_vdev_async_write_active_min_dirty_percent \|\|
	+ txg_sync_waiting(scn->scn_dp) \|\|
	+ NSEC2SEC(sync_time_ns) >= zfs_txg_timeout)) \|\|
	+ spa_shutting_down(scn->scn_dp->dp_spa));
	+}
	+
	+/*
	+ * Given a list of scan_io_t's in io_list, this issues the io's out to
	+ * disk. This consumes the io_list and frees the scan_io_t's. This is
	+ * called when emptying queues, either when we're up against the memory
	+ * limit or when we have finished scanning. Returns B_TRUE if we stopped
	+ * processing the list before we finished. Any zios that were not issued
	+ * will remain in the io_list.
	+ */
	+static boolean_t
	+scan_io_queue_issue(dsl_scan_io_queue_t queue, list_t io_list)
	+{
	+ dsl_scan_t *scn = queue->q_scn;
	+ scan_io_t *sio;
	+ int64_t bytes_issued = 0;
	+ boolean_t suspended = B_FALSE;
	+
	+ while ((sio = list_head(io_list)) != NULL) {
	+ blkptr_t bp;
	+
	+ if (scan_io_queue_check_suspend(scn)) {
	+ suspended = B_TRUE;
	+ break;
	+ }
	+
	+ sio2bp(sio, &bp, queue->q_vd->vdev_id);
	+ bytes_issued += sio->sio_asize;
	+ scan_exec_io(scn->scn_dp, &bp, sio->sio_flags,
	+ &sio->sio_zb, queue);
	+ (void) list_remove_head(io_list);
	+ scan_io_queues_update_zio_stats(queue, &bp);
	+ kmem_free(sio, sizeof (*sio));
	+ }
	+
	+ atomic_add_64(&scn->scn_bytes_pending, -bytes_issued);
	+
	+ return (suspended);
	+}
	+
	+/*
	+ * Given a range_seg_t (extent) and a list, this function passes over a
	+ * scan queue and gathers up the appropriate ios which fit into that
	+ * scan seg (starting from lowest LBA). At the end, we remove the segment
	+ * from the q_exts_by_addr range tree.
	+ */
	+static boolean_t
	+scan_io_queue_gather(dsl_scan_io_queue_t queue, range_seg_t rs, list_t *list)
	+{
	+ scan_io_t srch_sio, sio, next_sio;
	+ avl_index_t idx;
	+ uint_t num_sios = 0;
	+ int64_t bytes_issued = 0;
	+
	+ ASSERT(rs != NULL);
	+ ASSERT(MUTEX_HELD(&queue->q_vd->vdev_scan_io_queue_lock));
	+
	+ srch_sio.sio_offset = rs->rs_start;
	+
	+ /*
	+ * The exact start of the extent might not contain any matching zios,
	+ * so if that's the case, examine the next one in the tree.
	+ */
	+ sio = avl_find(&queue->q_sios_by_addr, &srch_sio, &idx);
	+ if (sio == NULL)
	+ sio = avl_nearest(&queue->q_sios_by_addr, idx, AVL_AFTER);
	+
	+ while (sio != NULL && sio->sio_offset < rs->rs_end && num_sios <= 32) {
	+ ASSERT3U(sio->sio_offset, >=, rs->rs_start);
	+ ASSERT3U(sio->sio_offset + sio->sio_asize, <=, rs->rs_end);
	+
	+ next_sio = AVL_NEXT(&queue->q_sios_by_addr, sio);
	+ avl_remove(&queue->q_sios_by_addr, sio);
	+
	+ bytes_issued += sio->sio_asize;
	+ num_sios++;
	+ list_insert_tail(list, sio);
	+ sio = next_sio;
	+ }
	+
	+ /*
	+ * We limit the number of sios we process at once to 32 to avoid
	+ * biting off more than we can chew. If we didn't take everything
	+ * in the segment we update it to reflect the work we were able to
	+ * complete. Otherwise, we remove it from the range tree entirely.
	+ */
	+ if (sio != NULL && sio->sio_offset < rs->rs_end) {
	+ range_tree_adjust_fill(queue->q_exts_by_addr, rs,
	+ -bytes_issued);
	+ range_tree_resize_segment(queue->q_exts_by_addr, rs,
	+ sio->sio_offset, rs->rs_end - sio->sio_offset);
	+
	+ return (B_TRUE);
	+ } else {
	+ range_tree_remove(queue->q_exts_by_addr, rs->rs_start,
	+ rs->rs_end - rs->rs_start);
	+ return (B_FALSE);
	+ }
	+}
	+
	+
	+/*
	+ * This is called from the queue emptying thread and selects the next
	+ * extent from which we are to issue io's. The behavior of this function
	+ * depends on the state of the scan, the current memory consumption and
	+ * whether or not we are performing a scan shutdown.
	+ * 1) We select extents in an elevator algorithm (LBA-order) if the scan
	+ * needs to perform a checkpoint
	+ * 2) We select the largest available extent if we are up against the
	+ * memory limit.
	+ * 3) Otherwise we don't select any extents.
	+ */
	+static const range_seg_t *
	+scan_io_queue_fetch_ext(dsl_scan_io_queue_t *queue)
	+{
	+ dsl_scan_t *scn = queue->q_scn;
	+
	+ ASSERT(MUTEX_HELD(&queue->q_vd->vdev_scan_io_queue_lock));
	+ ASSERT(scn->scn_is_sorted);
	+
	+ /* handle tunable overrides */
	+ if (scn->scn_checkpointing \|\| scn->scn_clearing) {
	+ if (zfs_scan_issue_strategy == 1) {
	+ return (range_tree_first(queue->q_exts_by_addr));
	+ } else if (zfs_scan_issue_strategy == 2) {
	+ return (avl_first(&queue->q_exts_by_size));
	+ }
	+ }
	+
	+ /*
	+ * During normal clearing, we want to issue our largest segments
	+ * first, keeping IO as sequential as possible, and leaving the
	+ * smaller extents for later with the hope that they might eventually
	+ * grow to larger sequential segments. However, when the scan is
	+ * checkpointing, no new extents will be added to the sorting queue,
	+ * so the way we are sorted now is as good as it will ever get.
	+ * In this case, we instead switch to issuing extents in LBA order.
	+ */
	+ if (scn->scn_checkpointing) {
	+ return (range_tree_first(queue->q_exts_by_addr));
	+ } else if (scn->scn_clearing) {
	+ return (avl_first(&queue->q_exts_by_size));
	+ } else {
	+ return (NULL);
	+ }
	+}
	+
	+static void
	+scan_io_queues_run_one(void *arg)
	+{
	+ dsl_scan_io_queue_t *queue = arg;
	+ kmutex_t *q_lock = &queue->q_vd->vdev_scan_io_queue_lock;
	+ boolean_t suspended = B_FALSE;
	+ range_seg_t *rs = NULL;
	+ scan_io_t *sio = NULL;
	+ list_t sio_list;
	+ uint64_t bytes_per_leaf = zfs_scan_vdev_limit;
	+ uint64_t nr_leaves = dsl_scan_count_leaves(queue->q_vd);
	+
	+ ASSERT(queue->q_scn->scn_is_sorted);
	+
	+ list_create(&sio_list, sizeof (scan_io_t),
	+ offsetof(scan_io_t, sio_nodes.sio_list_node));
	+ mutex_enter(q_lock);
	+
	+ /* calculate maximum in-flight bytes for this txg (min 1MB) */
	+ queue->q_maxinflight_bytes =
	+ MAX(nr_leaves * bytes_per_leaf, 1ULL << 20);
	+
	+ /* reset per-queue scan statistics for this txg */
	+ queue->q_total_seg_size_this_txg = 0;
	+ queue->q_segs_this_txg = 0;
	+ queue->q_total_zio_size_this_txg = 0;
	+ queue->q_zios_this_txg = 0;
	+
	+ /* loop until we have run out of time or sios */
	+ while ((rs = (range_seg_t*)scan_io_queue_fetch_ext(queue)) != NULL) {
	+ uint64_t seg_start = 0, seg_end = 0;
	+ boolean_t more_left = B_TRUE;
	+
	+ ASSERT(list_is_empty(&sio_list));
	+
	+ /* loop while we still have sios left to process in this rs */
	+ while (more_left) {
	+ scan_io_t first_sio, last_sio;
	+
	+ /*
	+ * We have selected which extent needs to be
	+ * processed next. Gather up the corresponding sios.
	+ */
	+ more_left = scan_io_queue_gather(queue, rs, &sio_list);
	+ ASSERT(!list_is_empty(&sio_list));
	+ first_sio = list_head(&sio_list);
	+ last_sio = list_tail(&sio_list);
	+
	+ seg_end = last_sio->sio_offset + last_sio->sio_asize;
	+ if (seg_start == 0)
	+ seg_start = first_sio->sio_offset;
	+
	+ /*
	+ * Issuing sios can take a long time so drop the
	+ * queue lock. The sio queue won't be updated by
	+ * other threads since we're in syncing context so
	+ * we can be sure that our trees will remain exactly
	+ * as we left them.
	+ */
	+ mutex_exit(q_lock);
	+ suspended = scan_io_queue_issue(queue, &sio_list);
	+ mutex_enter(q_lock);
	+
	+ if (suspended)
	+ break;
	+ }
	+ /* update statistics for debugging purposes */
	+ scan_io_queues_update_seg_stats(queue, seg_start, seg_end);
	+
	+ if (suspended)
	+ break;
	+ }
	+
	+
	+ /* If we were suspended in the middle of processing,
	+ * requeue any unfinished sios and exit.
	+ */
	+ while ((sio = list_head(&sio_list)) != NULL) {
	+ list_remove(&sio_list, sio);
	+ scan_io_queue_insert_impl(queue, sio);
	+ }
	+
	+ mutex_exit(q_lock);
	+ list_destroy(&sio_list);
	+}
	+
	+/*
	+ * Performs an emptying run on all scan queues in the pool. This just
	+ * punches out one thread per top-level vdev, each of which processes
	+ * only that vdev's scan queue. We can parallelize the I/O here because
	+ * we know that each queue's io's only affect its own top-level vdev.
	+ *
	+ * This function waits for the queue runs to complete, and must be
	+ * called from dsl_scan_sync (or in general, syncing context).
	+ */
	+static void
	+scan_io_queues_run(dsl_scan_t *scn)
	+{
	+ spa_t *spa = scn->scn_dp->dp_spa;
	+
	+ ASSERT(scn->scn_is_sorted);
	+ ASSERT(spa_config_held(spa, SCL_CONFIG, RW_READER));
	+
	+ if (scn->scn_bytes_pending == 0)
	+ return;
	+
	+ if (scn->scn_taskq == NULL) {
	+ char *tq_name = kmem_zalloc(ZFS_MAX_DATASET_NAME_LEN + 16,
	+ KM_SLEEP);
	+ int nthreads = spa->spa_root_vdev->vdev_children;
	+
	+ /*
	+ * We need to make this taskq always execute as many
	+ * threads in parallel as we have top-level vdevs and no
	+ * less, otherwise strange serialization of the calls to
	+ * scan_io_queues_run_one can occur during spa_sync runs
	+ * and that significantly impacts performance.
	+ */
	+ (void) snprintf(tq_name, ZFS_MAX_DATASET_NAME_LEN + 16,
	+ "dsl_scan_tq_%s", spa->spa_name);
	+ scn->scn_taskq = taskq_create(tq_name, nthreads, minclsyspri,
	+ nthreads, nthreads, TASKQ_PREPOPULATE);
	+ kmem_free(tq_name, ZFS_MAX_DATASET_NAME_LEN + 16);
	+ }
	+
	+ for (uint64_t i = 0; i < spa->spa_root_vdev->vdev_children; i++) {
	+ vdev_t *vd = spa->spa_root_vdev->vdev_child[i];
	+
	+ mutex_enter(&vd->vdev_scan_io_queue_lock);
	+ if (vd->vdev_scan_io_queue != NULL) {
	+ VERIFY(taskq_dispatch(scn->scn_taskq,
	+ scan_io_queues_run_one, vd->vdev_scan_io_queue,
	+ TQ_SLEEP) != TASKQID_INVALID);
	+ }
	+ mutex_exit(&vd->vdev_scan_io_queue_lock);
	+ }
	+
	+ /*
	+ * Wait for the queues to finish issuing thir IOs for this run
	+ * before we return. There may still be IOs in flight at this
	+ * point.
	+ */
	+ taskq_wait(scn->scn_taskq);
	+}
	+
	+static boolean_t
	dsl_scan_async_block_should_pause(dsl_scan_t *scn)
	{
	uint64_t elapsed_nanosecs;
	@@ -1581,6 +2894,41 @@
	return (0);
	}

	+static void
	+dsl_scan_update_stats(dsl_scan_t *scn)
	+{
	+ spa_t *spa = scn->scn_dp->dp_spa;
	+ uint64_t i;
	+ uint64_t seg_size_total = 0, zio_size_total = 0;
	+ uint64_t seg_count_total = 0, zio_count_total = 0;
	+
	+ for (i = 0; i < spa->spa_root_vdev->vdev_children; i++) {
	+ vdev_t *vd = spa->spa_root_vdev->vdev_child[i];
	+ dsl_scan_io_queue_t *queue = vd->vdev_scan_io_queue;
	+
	+ if (queue == NULL)
	+ continue;
	+
	+ seg_size_total += queue->q_total_seg_size_this_txg;
	+ zio_size_total += queue->q_total_zio_size_this_txg;
	+ seg_count_total += queue->q_segs_this_txg;
	+ zio_count_total += queue->q_zios_this_txg;
	+ }
	+
	+ if (seg_count_total == 0 \|\| zio_count_total == 0) {
	+ scn->scn_avg_seg_size_this_txg = 0;
	+ scn->scn_avg_zio_size_this_txg = 0;
	+ scn->scn_segs_this_txg = 0;
	+ scn->scn_zios_this_txg = 0;
	+ return;
	+ }
	+
	+ scn->scn_avg_seg_size_this_txg = seg_size_total / seg_count_total;
	+ scn->scn_avg_zio_size_this_txg = zio_size_total / zio_count_total;
	+ scn->scn_segs_this_txg = seg_count_total;
	+ scn->scn_zios_this_txg = zio_count_total;
	+}
	+
	boolean_t
	dsl_scan_active(dsl_scan_t *scn)
	{
	@@ -1591,8 +2939,7 @@
	return (B_FALSE);
	if (spa_shutting_down(spa))
	return (B_FALSE);
	- if ((scn->scn_phys.scn_state == DSS_SCANNING &&
	- !dsl_scan_is_paused_scrub(scn)) \|\|
	+ if ((dsl_scan_is_running(scn) && !dsl_scan_is_paused_scrub(scn)) \|\|
	(scn->scn_async_destroying && !scn->scn_async_stalled))
	return (B_TRUE);

	@@ -1614,14 +2961,15 @@
	return (0);

	if (zfs_free_bpobj_enabled &&
	- spa_version(dp->dp_spa) >= SPA_VERSION_DEADLISTS) {
	+ spa_version(spa) >= SPA_VERSION_DEADLISTS) {
	scn->scn_is_bptree = B_FALSE;
	scn->scn_async_block_min_time_ms = zfs_free_min_time_ms;
	- scn->scn_zio_root = zio_root(dp->dp_spa, NULL,
	+ scn->scn_zio_root = zio_root(spa, NULL,
	NULL, ZIO_FLAG_MUSTSUCCEED);
	err = bpobj_iterate(&dp->dp_free_bpobj,
	dsl_scan_free_block_cb, scn, tx);
	- VERIFY3U(0, ==, zio_wait(scn->scn_zio_root));
	+ VERIFY0(zio_wait(scn->scn_zio_root));
	+ scn->scn_zio_root = NULL;

	if (err != 0 && err != ERESTART)
	zfs_panic_recover("error %u from bpobj_iterate()", err);
	@@ -1630,11 +2978,12 @@
	if (err == 0 && spa_feature_is_active(spa, SPA_FEATURE_ASYNC_DESTROY)) {
	ASSERT(scn->scn_async_destroying);
	scn->scn_is_bptree = B_TRUE;
	- scn->scn_zio_root = zio_root(dp->dp_spa, NULL,
	+ scn->scn_zio_root = zio_root(spa, NULL,
	NULL, ZIO_FLAG_MUSTSUCCEED);
	err = bptree_iterate(dp->dp_meta_objset,
	dp->dp_bptree_obj, B_TRUE, dsl_scan_free_block_cb, scn, tx);
	VERIFY0(zio_wait(scn->scn_zio_root));
	+ scn->scn_zio_root = NULL;

	if (err == EIO \|\| err == ECKSUM) {
	err = 0;
	@@ -1743,12 +3092,60 @@
	return (0);
	}

	+static boolean_t
	+dsl_scan_need_resilver(spa_t spa, const dva_t dva, size_t psize,
	+ uint64_t phys_birth)
	+{
	+ vdev_t *vd;
	+
	+ if (DVA_GET_GANG(dva)) {
	+ /*
	+ * Gang members may be spread across multiple
	+ * vdevs, so the best estimate we have is the
	+ * scrub range, which has already been checked.
	+ * XXX -- it would be better to change our
	+ * allocation policy to ensure that all
	+ * gang members reside on the same vdev.
	+ */
	+ return (B_TRUE);
	+ }
	+
	+ vd = vdev_lookup_top(spa, DVA_GET_VDEV(dva));
	+
	+ /*
	+ * Check if the txg falls within the range which must be
	+ * resilvered. DVAs outside this range can always be skipped.
	+ */
	+ if (!vdev_dtl_contains(vd, DTL_PARTIAL, phys_birth, 1))
	+ return (B_FALSE);
	+
	+ /*
	+ * Check if the top-level vdev must resilver this offset.
	+ * When the offset does not intersect with a dirty leaf DTL
	+ * then it may be possible to skip the resilver IO. The psize
	+ * is provided instead of asize to simplify the check for RAIDZ.
	+ */
	+ if (!vdev_dtl_need_resilver(vd, DVA_GET_OFFSET(dva), psize))
	+ return (B_FALSE);
	+
	+ return (B_TRUE);
	+}
	+
	+/*
	+ * This is the primary entry point for scans that is called from syncing
	+ * context. Scans must happen entirely during syncing context so that we
	+ * cna guarantee that blocks we are currently scanning will not change out
	+ * from under us. While a scan is active, this funciton controls how quickly
	+ * transaction groups proceed, instead of the normal handling provided by
	+ * txg_sync_thread().
	+ */
	void
	dsl_scan_sync(dsl_pool_t dp, dmu_tx_t tx)
	{
	+ int err = 0;
	dsl_scan_t *scn = dp->dp_scan;
	spa_t *spa = dp->dp_spa;
	- int err = 0;
	+ state_sync_type_t sync_type = SYNC_OPTIONAL;

	/*
	* Check for scn_restart_txg before checking spa_load_state, so
	@@ -1761,7 +3158,7 @@
	if (vdev_resilver_needed(spa->spa_root_vdev, NULL, NULL))
	func = POOL_SCAN_RESILVER;
	zfs_dbgmsg("restarting scan func=%u txg=%llu",
	- func, tx->tx_txg);
	+ func, (longlong_t)tx->tx_txg);
	dsl_scan_setup_sync(&func, tx);
	}

	@@ -1785,7 +3182,17 @@
	if (!scn->scn_async_stalled && !dsl_scan_active(scn))
	return;

	+ /* reset scan statistics */
	scn->scn_visited_this_txg = 0;
	+ scn->scn_holes_this_txg = 0;
	+ scn->scn_lt_min_this_txg = 0;
	+ scn->scn_gt_max_this_txg = 0;
	+ scn->scn_ddt_contained_this_txg = 0;
	+ scn->scn_objsets_visited_this_txg = 0;
	+ scn->scn_avg_seg_size_this_txg = 0;
	+ scn->scn_segs_this_txg = 0;
	+ scn->scn_avg_zio_size_this_txg = 0;
	+ scn->scn_zios_this_txg = 0;
	scn->scn_suspending = B_FALSE;
	scn->scn_sync_start_time = gethrtime();
	spa->spa_scrub_active = B_TRUE;
	@@ -1801,110 +3208,189 @@
	if (err != 0)
	return;

	- if (scn->scn_phys.scn_state != DSS_SCANNING)
	+ if (!dsl_scan_is_running(scn) \|\| dsl_scan_is_paused_scrub(scn))
	return;

	- if (scn->scn_done_txg == tx->tx_txg) {
	- ASSERT(!scn->scn_suspending);
	- /* finished with scan. */
	- zfs_dbgmsg("txg %llu scan complete", tx->tx_txg);
	- dsl_scan_done(scn, B_TRUE, tx);
	- ASSERT3U(spa->spa_scrub_inflight, ==, 0);
	- dsl_scan_sync_state(scn, tx);
	+ /*
	+ * Wait a few txgs after importing to begin scanning so that
	+ * we can get the pool imported quickly.
	+ */
	+ if (spa->spa_syncing_txg < spa->spa_first_txg + SCAN_IMPORT_WAIT_TXGS)
	return;
	+
	+ /*
	+ * It is possible to switch from unsorted to sorted at any time,
	+ * but afterwards the scan will remain sorted unless reloaded from
	+ * a checkpoint after a reboot.
	+ */
	+ if (!zfs_scan_legacy) {
	+ scn->scn_is_sorted = B_TRUE;
	+ if (scn->scn_last_checkpoint == 0)
	+ scn->scn_last_checkpoint = ddi_get_lbolt();
	}

	- if (dsl_scan_is_paused_scrub(scn))
	- return;
	+ /*
	+ * For sorted scans, determine what kind of work we will be doing
	+ * this txg based on our memory limitations and whether or not we
	+ * need to perform a checkpoint.
	+ */
	+ if (scn->scn_is_sorted) {
	+ /*
	+ * If we are over our checkpoint interval, set scn_clearing
	+ * so that we can begin checkpointing immediately. The
	+ * checkpoint allows us to save a consisent bookmark
	+ * representing how much data we have scrubbed so far.
	+ * Otherwise, use the memory limit to determine if we should
	+ * scan for metadata or start issue scrub IOs. We accumulate
	+ * metadata until we hit our hard memory limit at which point
	+ * we issue scrub IOs until we are at our soft memory limit.
	+ */
	+ if (scn->scn_checkpointing \|\|
	+ ddi_get_lbolt() - scn->scn_last_checkpoint >
	+ SEC_TO_TICK(zfs_scan_checkpoint_intval)) {
	+ if (!scn->scn_checkpointing)
	+ zfs_dbgmsg("begin scan checkpoint");

	- if (scn->scn_phys.scn_ddt_bookmark.ddb_class <=
	- scn->scn_phys.scn_ddt_class_max) {
	- zfs_dbgmsg("doing scan sync txg %llu; "
	- "ddt bm=%llu/%llu/%llu/%llx",
	- (longlong_t)tx->tx_txg,
	- (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_class,
	- (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_type,
	- (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_checksum,
	- (longlong_t)scn->scn_phys.scn_ddt_bookmark.ddb_cursor);
	- ASSERT(scn->scn_phys.scn_bookmark.zb_objset == 0);
	- ASSERT(scn->scn_phys.scn_bookmark.zb_object == 0);
	- ASSERT(scn->scn_phys.scn_bookmark.zb_level == 0);
	- ASSERT(scn->scn_phys.scn_bookmark.zb_blkid == 0);
	+ scn->scn_checkpointing = B_TRUE;
	+ scn->scn_clearing = B_TRUE;
	+ } else {
	+ boolean_t should_clear = dsl_scan_should_clear(scn);
	+ if (should_clear && !scn->scn_clearing) {
	+ zfs_dbgmsg("begin scan clearing");
	+ scn->scn_clearing = B_TRUE;
	+ } else if (!should_clear && scn->scn_clearing) {
	+ zfs_dbgmsg("finish scan clearing");
	+ scn->scn_clearing = B_FALSE;
	+ }
	+ }
	} else {
	- zfs_dbgmsg("doing scan sync txg %llu; bm=%llu/%llu/%llu/%llu",
	- (longlong_t)tx->tx_txg,
	- (longlong_t)scn->scn_phys.scn_bookmark.zb_objset,
	- (longlong_t)scn->scn_phys.scn_bookmark.zb_object,
	- (longlong_t)scn->scn_phys.scn_bookmark.zb_level,
	- (longlong_t)scn->scn_phys.scn_bookmark.zb_blkid);
	+ ASSERT0(scn->scn_checkpointing);
	+ ASSERT0(scn->scn_clearing);
	}

	- scn->scn_zio_root = zio_root(dp->dp_spa, NULL,
	- NULL, ZIO_FLAG_CANFAIL);
	- dsl_pool_config_enter(dp, FTAG);
	- dsl_scan_visit(scn, tx);
	- dsl_pool_config_exit(dp, FTAG);
	- (void) zio_wait(scn->scn_zio_root);
	- scn->scn_zio_root = NULL;
	+ if (!scn->scn_clearing && scn->scn_done_txg == 0) {
	+ /* Need to scan metadata for more blocks to scrub */
	+ dsl_scan_phys_t *scnp = &scn->scn_phys;
	+ taskqid_t prefetch_tqid;
	+ uint64_t bytes_per_leaf = zfs_scan_vdev_limit;
	+ uint64_t nr_leaves = dsl_scan_count_leaves(spa->spa_root_vdev);

	- zfs_dbgmsg("visited %llu blocks in %llums",
	- (longlong_t)scn->scn_visited_this_txg,
	- (longlong_t)NSEC2MSEC(gethrtime() - scn->scn_sync_start_time));
	+ /*
	+ * Calculate the max number of in-flight bytes for pool-wide
	+ * scanning operations (minimum 1MB). Limits for the issuing
	+ * phase are done per top-level vdev and are handled separately.
	+ */
	+ scn->scn_maxinflight_bytes =
	+ MAX(nr_leaves * bytes_per_leaf, 1ULL << 20);

	- if (!scn->scn_suspending) {
	- scn->scn_done_txg = tx->tx_txg + 1;
	- zfs_dbgmsg("txg %llu traversal complete, waiting till txg %llu",
	- tx->tx_txg, scn->scn_done_txg);
	- }
	-
	- if (DSL_SCAN_IS_SCRUB_RESILVER(scn)) {
	- mutex_enter(&spa->spa_scrub_lock);
	- while (spa->spa_scrub_inflight > 0) {
	- cv_wait(&spa->spa_scrub_io_cv,
	- &spa->spa_scrub_lock);
	+ if (scnp->scn_ddt_bookmark.ddb_class <=
	+ scnp->scn_ddt_class_max) {
	+ ASSERT(ZB_IS_ZERO(&scnp->scn_bookmark));
	+ zfs_dbgmsg("doing scan sync txg %llu; "
	+ "ddt bm=%llu/%llu/%llu/%llx",
	+ (longlong_t)tx->tx_txg,
	+ (longlong_t)scnp->scn_ddt_bookmark.ddb_class,
	+ (longlong_t)scnp->scn_ddt_bookmark.ddb_type,
	+ (longlong_t)scnp->scn_ddt_bookmark.ddb_checksum,
	+ (longlong_t)scnp->scn_ddt_bookmark.ddb_cursor);
	+ } else {
	+ zfs_dbgmsg("doing scan sync txg %llu; "
	+ "bm=%llu/%llu/%llu/%llu",
	+ (longlong_t)tx->tx_txg,
	+ (longlong_t)scnp->scn_bookmark.zb_objset,
	+ (longlong_t)scnp->scn_bookmark.zb_object,
	+ (longlong_t)scnp->scn_bookmark.zb_level,
	+ (longlong_t)scnp->scn_bookmark.zb_blkid);
	}
	- mutex_exit(&spa->spa_scrub_lock);
	- }

	- dsl_scan_sync_state(scn, tx);
	-}
	+ scn->scn_zio_root = zio_root(dp->dp_spa, NULL,
	+ NULL, ZIO_FLAG_CANFAIL);

	-/*
	- * This will start a new scan, or restart an existing one.
	- */
	-void
	-dsl_resilver_restart(dsl_pool_t *dp, uint64_t txg)
	-{
	- if (txg == 0) {
	- dmu_tx_t *tx;
	- tx = dmu_tx_create_dd(dp->dp_mos_dir);
	- VERIFY(0 == dmu_tx_assign(tx, TXG_WAIT));
	+ scn->scn_prefetch_stop = B_FALSE;
	+ prefetch_tqid = taskq_dispatch(dp->dp_sync_taskq,
	+ dsl_scan_prefetch_thread, scn, TQ_SLEEP);
	+ ASSERT(prefetch_tqid != TASKQID_INVALID);

	- txg = dmu_tx_get_txg(tx);
	- dp->dp_scan->scn_restart_txg = txg;
	- dmu_tx_commit(tx);
	- } else {
	- dp->dp_scan->scn_restart_txg = txg;
	+ dsl_pool_config_enter(dp, FTAG);
	+ dsl_scan_visit(scn, tx);
	+ dsl_pool_config_exit(dp, FTAG);
	+
	+ mutex_enter(&dp->dp_spa->spa_scrub_lock);
	+ scn->scn_prefetch_stop = B_TRUE;
	+ cv_broadcast(&spa->spa_scrub_io_cv);
	+ mutex_exit(&dp->dp_spa->spa_scrub_lock);
	+
	+ taskq_wait_id(dp->dp_sync_taskq, prefetch_tqid);
	+ (void) zio_wait(scn->scn_zio_root);
	+ scn->scn_zio_root = NULL;
	+
	+ zfs_dbgmsg("scan visited %llu blocks in %llums "
	+ "(%llu os's, %llu holes, %llu < mintxg, "
	+ "%llu in ddt, %llu > maxtxg)",
	+ (longlong_t)scn->scn_visited_this_txg,
	+ (longlong_t)NSEC2MSEC(gethrtime() -
	+ scn->scn_sync_start_time),
	+ (longlong_t)scn->scn_objsets_visited_this_txg,
	+ (longlong_t)scn->scn_holes_this_txg,
	+ (longlong_t)scn->scn_lt_min_this_txg,
	+ (longlong_t)scn->scn_ddt_contained_this_txg,
	+ (longlong_t)scn->scn_gt_max_this_txg);
	+
	+ if (!scn->scn_suspending) {
	+ ASSERT0(avl_numnodes(&scn->scn_queue));
	+ scn->scn_done_txg = tx->tx_txg + 1;
	+ if (scn->scn_is_sorted) {
	+ scn->scn_checkpointing = B_TRUE;
	+ scn->scn_clearing = B_TRUE;
	+ }
	+ zfs_dbgmsg("scan complete txg %llu",
	+ (longlong_t)tx->tx_txg);
	+ }
	+ } else if (scn->scn_is_sorted && scn->scn_bytes_pending != 0) {
	+ /* need to issue scrubbing IOs from per-vdev queues */
	+ scn->scn_zio_root = zio_root(dp->dp_spa, NULL,
	+ NULL, ZIO_FLAG_CANFAIL);
	+ scan_io_queues_run(scn);
	+ (void) zio_wait(scn->scn_zio_root);
	+ scn->scn_zio_root = NULL;
	+
	+ /* calculate and dprintf the current memory usage */
	+ (void) dsl_scan_should_clear(scn);
	+ dsl_scan_update_stats(scn);
	+
	+ zfs_dbgmsg("scrubbed %llu blocks (%llu segs) in %llums "
	+ "(avg_block_size = %llu, avg_seg_size = %llu)",
	+ (longlong_t)scn->scn_zios_this_txg,
	+ (longlong_t)scn->scn_segs_this_txg,
	+ (longlong_t)NSEC2MSEC(gethrtime() -
	+ scn->scn_sync_start_time),
	+ (longlong_t)scn->scn_avg_zio_size_this_txg,
	+ (longlong_t)scn->scn_avg_seg_size_this_txg);
	+ } else if (scn->scn_done_txg != 0 && scn->scn_done_txg <= tx->tx_txg) {
	+ /* Finished with everything. Mark the scrub as complete */
	+ zfs_dbgmsg("scan issuing complete txg %llu",
	+ (longlong_t)tx->tx_txg);
	+ ASSERT3U(scn->scn_done_txg, !=, 0);
	+ ASSERT0(spa->spa_scrub_inflight);
	+ ASSERT0(scn->scn_bytes_pending);
	+ dsl_scan_done(scn, B_TRUE, tx);
	+ sync_type = SYNC_MANDATORY;
	}
	- zfs_dbgmsg("restarting resilver txg=%llu", txg);
	-}

	-boolean_t
	-dsl_scan_resilvering(dsl_pool_t *dp)
	-{
	- return (dp->dp_scan->scn_phys.scn_state == DSS_SCANNING &&
	- dp->dp_scan->scn_phys.scn_func == POOL_SCAN_RESILVER);
	+ dsl_scan_sync_state(scn, tx, sync_type);
	}

	-/*
	- * scrub consumers
	- */
	-
	static void
	-count_block(zfs_all_blkstats_t zab, const blkptr_t bp)
	+count_block(dsl_scan_t scn, zfs_all_blkstats_t zab, const blkptr_t *bp)
	{
	int i;

	+ /* update the spa's stats on how many bytes we have issued */
	+ for (i = 0; i < BP_GET_NDVAS(bp); i++) {
	+ atomic_add_64(&scn->scn_dp->dp_spa->spa_scan_pass_issued,
	+ DVA_GET_ASIZE(&bp->blk_dva[i]));
	+ }
	+
	/*
	* If we resume after a reboot, zab will be NULL; don't record
	* incomplete stats in that case.
	@@ -1912,6 +3398,8 @@
	if (zab == NULL)
	return;

	+ mutex_enter(&zab->zab_lock);
	+
	for (i = 0; i < 4; i++) {
	int l = (i < 2) ? BP_GET_LEVEL(bp) : DN_MAX_LEVELS;
	int t = (i & 1) ? BP_GET_TYPE(bp) : DMU_OT_TOTAL;
	@@ -1946,24 +3434,96 @@
	break;
	}
	}
	+
	+ mutex_exit(&zab->zab_lock);
	}

	static void
	-dsl_scan_scrub_done(zio_t *zio)
	+scan_io_queue_insert_impl(dsl_scan_io_queue_t queue, scan_io_t sio)
	{
	- spa_t *spa = zio->io_spa;
	+ avl_index_t idx;
	+ int64_t asize = sio->sio_asize;
	+ dsl_scan_t *scn = queue->q_scn;

	- abd_free(zio->io_abd);
	+ ASSERT(MUTEX_HELD(&queue->q_vd->vdev_scan_io_queue_lock));

	- mutex_enter(&spa->spa_scrub_lock);
	- spa->spa_scrub_inflight--;
	- cv_broadcast(&spa->spa_scrub_io_cv);
	+ if (avl_find(&queue->q_sios_by_addr, sio, &idx) != NULL) {
	+ /* block is already scheduled for reading */
	+ atomic_add_64(&scn->scn_bytes_pending, -asize);
	+ kmem_free(sio, sizeof (*sio));
	+ return;
	+ }
	+ avl_insert(&queue->q_sios_by_addr, sio, idx);
	+ range_tree_add(queue->q_exts_by_addr, sio->sio_offset, asize);
	+}

	- if (zio->io_error && (zio->io_error != ECKSUM \|\|
	- !(zio->io_flags & ZIO_FLAG_SPECULATIVE))) {
	- spa->spa_dsl_pool->dp_scan->scn_phys.scn_errors++;
	+/*
	+ * Given all the info we got from our metadata scanning process, we
	+ * construct a scan_io_t and insert it into the scan sorting queue. The
	+ * I/O must already be suitable for us to process. This is controlled
	+ * by dsl_scan_enqueue().
	+ */
	+static void
	+scan_io_queue_insert(dsl_scan_io_queue_t queue, const blkptr_t bp, int dva_i,
	+ int zio_flags, const zbookmark_phys_t *zb)
	+{
	+ dsl_scan_t *scn = queue->q_scn;
	+ scan_io_t sio = kmem_zalloc(sizeof (sio), KM_SLEEP);
	+
	+ ASSERT0(BP_IS_GANG(bp));
	+ ASSERT(MUTEX_HELD(&queue->q_vd->vdev_scan_io_queue_lock));
	+
	+ bp2sio(bp, sio, dva_i);
	+ sio->sio_flags = zio_flags;
	+ sio->sio_zb = *zb;
	+
	+ /*
	+ * Increment the bytes pending counter now so that we can't
	+ * get an integer underflow in case the worker processes the
	+ * zio before we get to incrementing this counter.
	+ */
	+ atomic_add_64(&scn->scn_bytes_pending, sio->sio_asize);
	+
	+ scan_io_queue_insert_impl(queue, sio);
	+}
	+
	+/*
	+ * Given a set of I/O parameters as discovered by the metadata traversal
	+ * process, attempts to place the I/O into the sorted queues (if allowed),
	+ * or immediately executes the I/O.
	+ */
	+static void
	+dsl_scan_enqueue(dsl_pool_t dp, const blkptr_t bp, int zio_flags,
	+ const zbookmark_phys_t *zb)
	+{
	+ spa_t *spa = dp->dp_spa;
	+
	+ ASSERT(!BP_IS_EMBEDDED(bp));
	+
	+ /*
	+ * Gang blocks are hard to issue sequentially, so we just issue them
	+ * here immediately instead of queuing them.
	+ */
	+ if (!dp->dp_scan->scn_is_sorted \|\| BP_IS_GANG(bp)) {
	+ scan_exec_io(dp, bp, zio_flags, zb, NULL);
	+ return;
	}
	- mutex_exit(&spa->spa_scrub_lock);
	+ for (int i = 0; i < BP_GET_NDVAS(bp); i++) {
	+ dva_t dva;
	+ vdev_t *vdev;
	+
	+ dva = bp->blk_dva[i];
	+ vdev = vdev_lookup_top(spa, DVA_GET_VDEV(&dva));
	+ ASSERT(vdev != NULL);
	+
	+ mutex_enter(&vdev->vdev_scan_io_queue_lock);
	+ if (vdev->vdev_scan_io_queue == NULL)
	+ vdev->vdev_scan_io_queue = scan_io_queue_create(vdev);
	+ ASSERT(dp->dp_scan != NULL);
	+ scan_io_queue_insert(vdev->vdev_scan_io_queue, bp,
	+ i, zio_flags, zb);
	+ mutex_exit(&vdev->vdev_scan_io_queue_lock);
	+ }
	}

	static int
	@@ -1971,137 +3531,390 @@
	const blkptr_t bp, const zbookmark_phys_t zb)
	{
	dsl_scan_t *scn = dp->dp_scan;
	- size_t size = BP_GET_PSIZE(bp);
	spa_t *spa = dp->dp_spa;
	uint64_t phys_birth = BP_PHYSICAL_BIRTH(bp);
	+ size_t psize = BP_GET_PSIZE(bp);
	boolean_t needs_io;
	int zio_flags = ZIO_FLAG_SCAN_THREAD \| ZIO_FLAG_RAW \| ZIO_FLAG_CANFAIL;
	- unsigned int scan_delay = 0;
	-
	+ int d;
	+
	if (phys_birth <= scn->scn_phys.scn_min_txg \|\|
	phys_birth >= scn->scn_phys.scn_max_txg)
	return (0);

	- count_block(dp->dp_blkstats, bp);
	-
	- if (BP_IS_EMBEDDED(bp))
	+ if (BP_IS_EMBEDDED(bp)) {
	+ count_block(scn, dp->dp_blkstats, bp);
	return (0);
	+ }

	ASSERT(DSL_SCAN_IS_SCRUB_RESILVER(scn));
	if (scn->scn_phys.scn_func == POOL_SCAN_SCRUB) {
	zio_flags \|= ZIO_FLAG_SCRUB;
	needs_io = B_TRUE;
	- scan_delay = zfs_scrub_delay;
	} else {
	ASSERT3U(scn->scn_phys.scn_func, ==, POOL_SCAN_RESILVER);
	zio_flags \|= ZIO_FLAG_RESILVER;
	needs_io = B_FALSE;
	- scan_delay = zfs_resilver_delay;
	}

	/* If it's an intent log block, failure is expected. */
	if (zb->zb_level == ZB_ZIL_LEVEL)
	zio_flags \|= ZIO_FLAG_SPECULATIVE;

	- for (int d = 0; d < BP_GET_NDVAS(bp); d++) {
	- vdev_t *vd = vdev_lookup_top(spa,
	- DVA_GET_VDEV(&bp->blk_dva[d]));
	+ for (d = 0; d < BP_GET_NDVAS(bp); d++) {
	+ const dva_t *dva = &bp->blk_dva[d];

	/*
	* Keep track of how much data we've examined so that
	* zpool(1M) status can make useful progress reports.
	*/
	- scn->scn_phys.scn_examined += DVA_GET_ASIZE(&bp->blk_dva[d]);
	- spa->spa_scan_pass_exam += DVA_GET_ASIZE(&bp->blk_dva[d]);
	+ scn->scn_phys.scn_examined += DVA_GET_ASIZE(dva);
	+ spa->spa_scan_pass_exam += DVA_GET_ASIZE(dva);

	/* if it's a resilver, this may not be in the target range */
	- if (!needs_io) {
	- if (DVA_GET_GANG(&bp->blk_dva[d])) {
	- /*
	- * Gang members may be spread across multiple
	- * vdevs, so the best estimate we have is the
	- * scrub range, which has already been checked.
	- * XXX -- it would be better to change our
	- * allocation policy to ensure that all
	- * gang members reside on the same vdev.
	- */
	- needs_io = B_TRUE;
	- } else {
	- needs_io = vdev_dtl_contains(vd, DTL_PARTIAL,
	- phys_birth, 1);
	- }
	- }
	+ if (!needs_io)
	+ needs_io = dsl_scan_need_resilver(spa, dva, psize,
	+ phys_birth);
	}

	if (needs_io && !zfs_no_scrub_io) {
	- vdev_t *rvd = spa->spa_root_vdev;
	- uint64_t maxinflight = rvd->vdev_children *
	- MAX(zfs_top_maxinflight, 1);
	+ dsl_scan_enqueue(dp, bp, zio_flags, zb);
	+ } else {
	+ count_block(scn, dp->dp_blkstats, bp);
	+ }

	+ /* do not relocate this block */
	+ return (0);
	+}
	+
	+static void
	+dsl_scan_scrub_done(zio_t *zio)
	+{
	+ spa_t *spa = zio->io_spa;
	+ blkptr_t *bp = zio->io_bp;
	+ dsl_scan_io_queue_t *queue = zio->io_private;
	+
	+ abd_free(zio->io_abd);
	+
	+ if (queue == NULL) {
	mutex_enter(&spa->spa_scrub_lock);
	- while (spa->spa_scrub_inflight >= maxinflight)
	+ ASSERT3U(spa->spa_scrub_inflight, >=, BP_GET_PSIZE(bp));
	+ spa->spa_scrub_inflight -= BP_GET_PSIZE(bp);
	+ cv_broadcast(&spa->spa_scrub_io_cv);
	+ mutex_exit(&spa->spa_scrub_lock);
	+ } else {
	+ mutex_enter(&queue->q_vd->vdev_scan_io_queue_lock);
	+ ASSERT3U(queue->q_inflight_bytes, >=, BP_GET_PSIZE(bp));
	+ queue->q_inflight_bytes -= BP_GET_PSIZE(bp);
	+ cv_broadcast(&queue->q_zio_cv);
	+ mutex_exit(&queue->q_vd->vdev_scan_io_queue_lock);
	+ }
	+
	+ if (zio->io_error && (zio->io_error != ECKSUM \|\|
	+ !(zio->io_flags & ZIO_FLAG_SPECULATIVE))) {
	+ atomic_inc_64(&spa->spa_dsl_pool->dp_scan->scn_phys.scn_errors);
	+ }
	+}
	+
	+/*
	+ * Given a scanning zio's information, executes the zio. The zio need
	+ * not necessarily be only sortable, this function simply executes the
	+ * zio, no matter what it is. The optional queue argument allows the
	+ * caller to specify that they want per top level vdev IO rate limiting
	+ * instead of the legacy global limiting.
	+ */
	+static void
	+scan_exec_io(dsl_pool_t dp, const blkptr_t bp, int zio_flags,
	+ const zbookmark_phys_t zb, dsl_scan_io_queue_t queue)
	+{
	+ spa_t *spa = dp->dp_spa;
	+ dsl_scan_t *scn = dp->dp_scan;
	+ size_t size = BP_GET_PSIZE(bp);
	+ abd_t *data = abd_alloc_for_io(size, B_FALSE);
	+ unsigned int scan_delay = 0;
	+
	+ if (queue == NULL) {
	+ mutex_enter(&spa->spa_scrub_lock);
	+ while (spa->spa_scrub_inflight >= scn->scn_maxinflight_bytes)
	cv_wait(&spa->spa_scrub_io_cv, &spa->spa_scrub_lock);
	- spa->spa_scrub_inflight++;
	+ spa->spa_scrub_inflight += BP_GET_PSIZE(bp);
	mutex_exit(&spa->spa_scrub_lock);
	+ } else {
	+ kmutex_t *q_lock = &queue->q_vd->vdev_scan_io_queue_lock;

	- /*
	- * If we're seeing recent (zfs_scan_idle) "important" I/Os
	- * then throttle our workload to limit the impact of a scan.
	- */
	- if (ddi_get_lbolt64() - spa->spa_last_io <= zfs_scan_idle)
	- delay(MAX((int)scan_delay, 0));
	+ mutex_enter(q_lock);
	+ while (queue->q_inflight_bytes >= queue->q_maxinflight_bytes)
	+ cv_wait(&queue->q_zio_cv, q_lock);
	+ queue->q_inflight_bytes += BP_GET_PSIZE(bp);
	+ mutex_exit(q_lock);
	+ }

	- zio_nowait(zio_read(NULL, spa, bp,
	- abd_alloc_for_io(size, B_FALSE), size, dsl_scan_scrub_done,
	- NULL, ZIO_PRIORITY_SCRUB, zio_flags, zb));
	+ if (zio_flags & ZIO_FLAG_RESILVER)
	+ scan_delay = zfs_resilver_delay;
	+ else {
	+ ASSERT(zio_flags & ZIO_FLAG_SCRUB);
	+ scan_delay = zfs_scrub_delay;
	}

	- /* do not relocate this block */
	- return (0);
	+ if (scan_delay && (ddi_get_lbolt64() - spa->spa_last_io <= zfs_scan_idle))
	+ delay(MAX((int)scan_delay, 0));
	+
	+ count_block(dp->dp_scan, dp->dp_blkstats, bp);
	+ zio_nowait(zio_read(dp->dp_scan->scn_zio_root, spa, bp, data, size,
	+ dsl_scan_scrub_done, queue, ZIO_PRIORITY_SCRUB, zio_flags, zb));
	}

	/*
	- * Called by the ZFS_IOC_POOL_SCAN ioctl to start a scrub or resilver.
	- * Can also be called to resume a paused scrub.
	+ * This is the primary extent sorting algorithm. We balance two parameters:
	+ * 1) how many bytes of I/O are in an extent
	+ * 2) how well the extent is filled with I/O (as a fraction of its total size)
	+ * Since we allow extents to have gaps between their constituent I/Os, it's
	+ * possible to have a fairly large extent that contains the same amount of
	+ * I/O bytes than a much smaller extent, which just packs the I/O more tightly.
	+ * The algorithm sorts based on a score calculated from the extent's size,
	+ * the relative fill volume (in %) and a "fill weight" parameter that controls
	+ * the split between whether we prefer larger extents or more well populated
	+ * extents:
	+ *
	+ * SCORE = FILL_IN_BYTES + (FILL_IN_PERCENT * FILL_IN_BYTES * FILL_WEIGHT)
	+ *
	+ * Example:
	+ * 1) assume extsz = 64 MiB
	+ * 2) assume fill = 32 MiB (extent is half full)
	+ * 3) assume fill_weight = 3
	+ * 4) SCORE = 32M + (((32M * 100) / 64M) * 3 * 32M) / 100
	+ * SCORE = 32M + (50 * 3 * 32M) / 100
	+ * SCORE = 32M + (4800M / 100)
	+ * SCORE = 32M + 48M
	+ * ^ ^
	+ * \| +--- final total relative fill-based score
	+ * +--------- final total fill-based score
	+ * SCORE = 80M
	+ *
	+ * As can be seen, at fill_ratio=3, the algorithm is slightly biased towards
	+ * extents that are more completely filled (in a 3:2 ratio) vs just larger.
	+ * Note that as an optimization, we replace multiplication and division by
	+ * 100 with bitshifting by 7 (which effecitvely multiplies and divides by 128).
	*/
	-int
	-dsl_scan(dsl_pool_t *dp, pool_scan_func_t func)
	+static int
	+ext_size_compare(const void x, const void y)
	{
	- spa_t *spa = dp->dp_spa;
	+ const range_seg_t rsa = x, rsb = y;
	+ uint64_t sa = rsa->rs_end - rsa->rs_start,
	+ sb = rsb->rs_end - rsb->rs_start;
	+ uint64_t score_a, score_b;
	+
	+ score_a = rsa->rs_fill + ((((rsa->rs_fill << 7) / sa) *
	+ fill_weight * rsa->rs_fill) >> 7);
	+ score_b = rsb->rs_fill + ((((rsb->rs_fill << 7) / sb) *
	+ fill_weight * rsb->rs_fill) >> 7);
	+
	+ if (score_a > score_b)
	+ return (-1);
	+ if (score_a == score_b) {
	+ if (rsa->rs_start < rsb->rs_start)
	+ return (-1);
	+ if (rsa->rs_start == rsb->rs_start)
	+ return (0);
	+ return (1);
	+ }
	+ return (1);
	+}
	+
	+/*
	+ * Comparator for the q_sios_by_addr tree. Sorting is simply performed
	+ * based on LBA-order (from lowest to highest).
	+ */
	+static int
	+io_addr_compare(const void x, const void y)
	+{
	+ const scan_io_t a = x, b = y;
	+
	+ if (a->sio_offset < b->sio_offset)
	+ return (-1);
	+ if (a->sio_offset == b->sio_offset)
	+ return (0);
	+ return (1);
	+}
	+
	+/* IO queues are created on demand when they are needed. */
	+static dsl_scan_io_queue_t *
	+scan_io_queue_create(vdev_t *vd)
	+{
	+ dsl_scan_t *scn = vd->vdev_spa->spa_dsl_pool->dp_scan;
	+ dsl_scan_io_queue_t q = kmem_zalloc(sizeof (q), KM_SLEEP);
	+
	+ q->q_scn = scn;
	+ q->q_vd = vd;
	+ cv_init(&q->q_zio_cv, NULL, CV_DEFAULT, NULL);
	+ q->q_exts_by_addr = range_tree_create_impl(&rt_avl_ops,
	+ &q->q_exts_by_size, ext_size_compare, zfs_scan_max_ext_gap);
	+ avl_create(&q->q_sios_by_addr, io_addr_compare,
	+ sizeof (scan_io_t), offsetof(scan_io_t, sio_nodes.sio_addr_node));
	+
	+ return (q);
	+}
	+
	+/*
	+ * Destroys a scan queue and all segments and scan_io_t's contained in it.
	+ * No further execution of I/O occurs, anything pending in the queue is
	+ * simply freed without being executed.
	+ */
	+void
	+dsl_scan_io_queue_destroy(dsl_scan_io_queue_t *queue)
	+{
	+ dsl_scan_t *scn = queue->q_scn;
	+ scan_io_t *sio;
	+ void *cookie = NULL;
	+ int64_t bytes_dequeued = 0;
	+
	+ ASSERT(MUTEX_HELD(&queue->q_vd->vdev_scan_io_queue_lock));
	+
	+ while ((sio = avl_destroy_nodes(&queue->q_sios_by_addr, &cookie)) !=
	+ NULL) {
	+ ASSERT(range_tree_contains(queue->q_exts_by_addr,
	+ sio->sio_offset, sio->sio_asize));
	+ bytes_dequeued += sio->sio_asize;
	+ kmem_free(sio, sizeof (*sio));
	+ }
	+
	+ atomic_add_64(&scn->scn_bytes_pending, -bytes_dequeued);
	+ range_tree_vacate(queue->q_exts_by_addr, NULL, queue);
	+ range_tree_destroy(queue->q_exts_by_addr);
	+ avl_destroy(&queue->q_sios_by_addr);
	+ cv_destroy(&queue->q_zio_cv);
	+
	+ kmem_free(queue, sizeof (*queue));
	+}
	+
	+/*
	+ * Properly transfers a dsl_scan_queue_t from `svd' to `tvd'. This is
	+ * called on behalf of vdev_top_transfer when creating or destroying
	+ * a mirror vdev due to zpool attach/detach.
	+ */
	+void
	+dsl_scan_io_queue_vdev_xfer(vdev_t svd, vdev_t tvd)
	+{
	+ mutex_enter(&svd->vdev_scan_io_queue_lock);
	+ mutex_enter(&tvd->vdev_scan_io_queue_lock);
	+
	+ VERIFY3P(tvd->vdev_scan_io_queue, ==, NULL);
	+ tvd->vdev_scan_io_queue = svd->vdev_scan_io_queue;
	+ svd->vdev_scan_io_queue = NULL;
	+ if (tvd->vdev_scan_io_queue != NULL)
	+ tvd->vdev_scan_io_queue->q_vd = tvd;
	+
	+ mutex_exit(&tvd->vdev_scan_io_queue_lock);
	+ mutex_exit(&svd->vdev_scan_io_queue_lock);
	+}
	+
	+static void
	+scan_io_queues_destroy(dsl_scan_t *scn)
	+{
	+ vdev_t *rvd = scn->scn_dp->dp_spa->spa_root_vdev;
	+
	+ for (uint64_t i = 0; i < rvd->vdev_children; i++) {
	+ vdev_t *tvd = rvd->vdev_child[i];
	+
	+ mutex_enter(&tvd->vdev_scan_io_queue_lock);
	+ if (tvd->vdev_scan_io_queue != NULL)
	+ dsl_scan_io_queue_destroy(tvd->vdev_scan_io_queue);
	+ tvd->vdev_scan_io_queue = NULL;
	+ mutex_exit(&tvd->vdev_scan_io_queue_lock);
	+ }
	+}
	+
	+static void
	+dsl_scan_freed_dva(spa_t spa, const blkptr_t bp, int dva_i)
	+{
	+ dsl_pool_t *dp = spa->spa_dsl_pool;
	dsl_scan_t *scn = dp->dp_scan;
	+ vdev_t *vdev;
	+ kmutex_t *q_lock;
	+ dsl_scan_io_queue_t *queue;
	+ scan_io_t srch, *sio;
	+ avl_index_t idx;
	+ uint64_t start, size;

	+ vdev = vdev_lookup_top(spa, DVA_GET_VDEV(&bp->blk_dva[dva_i]));
	+ ASSERT(vdev != NULL);
	+ q_lock = &vdev->vdev_scan_io_queue_lock;
	+ queue = vdev->vdev_scan_io_queue;
	+
	+ mutex_enter(q_lock);
	+ if (queue == NULL) {
	+ mutex_exit(q_lock);
	+ return;
	+ }
	+
	+ bp2sio(bp, &srch, dva_i);
	+ start = srch.sio_offset;
	+ size = srch.sio_asize;
	+
	/*
	- * Purge all vdev caches and probe all devices. We do this here
	- * rather than in sync context because this requires a writer lock
	- * on the spa_config lock, which we can't do from sync context. The
	- * spa_scrub_reopen flag indicates that vdev_open() should not
	- * attempt to start another scrub.
	+ * We can find the zio in two states:
	+ * 1) Cold, just sitting in the queue of zio's to be issued at
	+ * some point in the future. In this case, all we do is
	+ * remove the zio from the q_sios_by_addr tree, decrement
	+ * its data volume from the containing range_seg_t and
	+ * resort the q_exts_by_size tree to reflect that the
	+ * range_seg_t has lost some of its 'fill'. We don't shorten
	+ * the range_seg_t - this is usually rare enough not to be
	+ * worth the extra hassle of trying keep track of precise
	+ * extent boundaries.
	+ * 2) Hot, where the zio is currently in-flight in
	+ * dsl_scan_issue_ios. In this case, we can't simply
	+ * reach in and stop the in-flight zio's, so we instead
	+ * block the caller. Eventually, dsl_scan_issue_ios will
	+ * be done with issuing the zio's it gathered and will
	+ * signal us.
	*/
	- spa_vdev_state_enter(spa, SCL_NONE);
	- spa->spa_scrub_reopen = B_TRUE;
	- vdev_reopen(spa->spa_root_vdev);
	- spa->spa_scrub_reopen = B_FALSE;
	- (void) spa_vdev_state_exit(spa, NULL, 0);
	+ sio = avl_find(&queue->q_sios_by_addr, &srch, &idx);
	+ if (sio != NULL) {
	+ int64_t asize = sio->sio_asize;
	+ blkptr_t tmpbp;

	- if (func == POOL_SCAN_SCRUB && dsl_scan_is_paused_scrub(scn)) {
	- /* got scrub start cmd, resume paused scrub */
	- int err = dsl_scrub_set_pause_resume(scn->scn_dp,
	- POOL_SCRUB_NORMAL);
	- if (err == 0) {
	- spa_event_notify(spa, NULL, NULL, ESC_ZFS_SCRUB_RESUME);
	- return (ECANCELED);
	- }
	+ /* Got it while it was cold in the queue */
	+ ASSERT3U(start, ==, sio->sio_offset);
	+ ASSERT3U(size, ==, asize);
	+ avl_remove(&queue->q_sios_by_addr, sio);

	- return (SET_ERROR(err));
	- }
	+ ASSERT(range_tree_contains(queue->q_exts_by_addr, start, size));
	+ range_tree_remove_fill(queue->q_exts_by_addr, start, size);

	- return (dsl_sync_task(spa_name(spa), dsl_scan_setup_check,
	- dsl_scan_setup_sync, &func, 0, ZFS_SPACE_CHECK_EXTRA_RESERVED));
	+ /*
	+ * We only update scn_bytes_pending in the cold path,
	+ * otherwise it will already have been accounted for as
	+ * part of the zio's execution.
	+ */
	+ atomic_add_64(&scn->scn_bytes_pending, -asize);
	+
	+ /* count the block as though we issued it */
	+ sio2bp(sio, &tmpbp, dva_i);
	+ count_block(scn, dp->dp_blkstats, &tmpbp);
	+
	+ kmem_free(sio, sizeof (*sio));
	+ }
	+ mutex_exit(q_lock);
	}

	-static boolean_t
	-dsl_scan_restarting(dsl_scan_t scn, dmu_tx_t tx)
	+/*
	+ * Callback invoked when a zio_free() zio is executing. This needs to be
	+ * intercepted to prevent the zio from deallocating a particular portion
	+ * of disk space and it then getting reallocated and written to, while we
	+ * still have it queued up for processing.
	+ */
	+void
	+dsl_scan_freed(spa_t spa, const blkptr_t bp)
	{
	- return (scn->scn_restart_txg != 0 &&
	- scn->scn_restart_txg <= tx->tx_txg);
	+ dsl_pool_t *dp = spa->spa_dsl_pool;
	+ dsl_scan_t *scn = dp->dp_scan;
	+
	+ ASSERT(!BP_IS_EMBEDDED(bp));
	+ ASSERT(scn != NULL);
	+ if (!dsl_scan_is_running(scn))
	+ return;
	+
	+ for (int i = 0; i < BP_GET_NDVAS(bp); i++)
	+ dsl_scan_freed_dva(spa, bp, i);
	}
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/metaslab.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/metaslab.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/metaslab.c
	@@ -1120,85 +1120,6 @@
	}

	/*
	- * Create any block allocator specific components. The current allocators
	- * rely on using both a size-ordered range_tree_t and an array of uint64_t's.
	- */
	-static void
	-metaslab_rt_create(range_tree_t rt, void arg)
	-{
	- metaslab_t *msp = arg;
	-
	- ASSERT3P(rt->rt_arg, ==, msp);
	- ASSERT(msp->ms_allocatable == NULL);
	-
	- avl_create(&msp->ms_allocatable_by_size, metaslab_rangesize_compare,
	- sizeof (range_seg_t), offsetof(range_seg_t, rs_pp_node));
	-}
	-
	-/*
	- * Destroy the block allocator specific components.
	- */
	-static void
	-metaslab_rt_destroy(range_tree_t rt, void arg)
	-{
	- metaslab_t *msp = arg;
	-
	- ASSERT3P(rt->rt_arg, ==, msp);
	- ASSERT3P(msp->ms_allocatable, ==, rt);
	- ASSERT0(avl_numnodes(&msp->ms_allocatable_by_size));
	-
	- avl_destroy(&msp->ms_allocatable_by_size);
	-}
	-
	-static void
	-metaslab_rt_add(range_tree_t rt, range_seg_t rs, void *arg)
	-{
	- metaslab_t *msp = arg;
	-
	- ASSERT3P(rt->rt_arg, ==, msp);
	- ASSERT3P(msp->ms_allocatable, ==, rt);
	- VERIFY(!msp->ms_condensing);
	- avl_add(&msp->ms_allocatable_by_size, rs);
	-}
	-
	-static void
	-metaslab_rt_remove(range_tree_t rt, range_seg_t rs, void *arg)
	-{
	- metaslab_t *msp = arg;
	-
	- ASSERT3P(rt->rt_arg, ==, msp);
	- ASSERT3P(msp->ms_allocatable, ==, rt);
	- VERIFY(!msp->ms_condensing);
	- avl_remove(&msp->ms_allocatable_by_size, rs);
	-}
	-
	-static void
	-metaslab_rt_vacate(range_tree_t rt, void arg)
	-{
	- metaslab_t *msp = arg;
	-
	- ASSERT3P(rt->rt_arg, ==, msp);
	- ASSERT3P(msp->ms_allocatable, ==, rt);
	-
	- /*
	- * Normally one would walk the tree freeing nodes along the way.
	- * Since the nodes are shared with the range trees we can avoid
	- * walking all nodes and just reinitialize the avl tree. The nodes
	- * will be freed by the range tree, so we don't want to free them here.
	- */
	- avl_create(&msp->ms_allocatable_by_size, metaslab_rangesize_compare,
	- sizeof (range_seg_t), offsetof(range_seg_t, rs_pp_node));
	-}
	-
	-static range_tree_ops_t metaslab_rt_ops = {
	- metaslab_rt_create,
	- metaslab_rt_destroy,
	- metaslab_rt_add,
	- metaslab_rt_remove,
	- metaslab_rt_vacate
	-};
	-
	-/*
	* ==========================================================================
	* Common allocator routines
	* ==========================================================================
	@@ -1574,7 +1495,8 @@
	* addition of new space; and for debugging, it ensures that we'd
	* data fault on any attempt to use this metaslab before it's ready.
	*/
	- ms->ms_allocatable = range_tree_create(&metaslab_rt_ops, ms);
	+ ms->ms_allocatable = range_tree_create_impl(&rt_avl_ops, &ms->ms_allocatable_by_size,
	+ metaslab_rangesize_compare, 0);
	metaslab_group_add(mg, ms);

	metaslab_set_fragmentation(ms);
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/range_tree.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/range_tree.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/range_tree.c
	@@ -33,8 +33,58 @@
	#include <sys/zio.h>
	#include <sys/range_tree.h>

	+/*
	+ * Range trees are tree-based data structures that can be used to
	+ * track free space or generally any space allocation information.
	+ * A range tree keeps track of individual segments and automatically
	+ * provides facilities such as adjacent extent merging and extent
	+ * splitting in response to range add/remove requests.
	+ *
	+ * A range tree starts out completely empty, with no segments in it.
	+ * Adding an allocation via range_tree_add to the range tree can either:
	+ * 1) create a new extent
	+ * 2) extend an adjacent extent
	+ * 3) merge two adjacent extents
	+ * Conversely, removing an allocation via range_tree_remove can:
	+ * 1) completely remove an extent
	+ * 2) shorten an extent (if the allocation was near one of its ends)
	+ * 3) split an extent into two extents, in effect punching a hole
	+ *
	+ * A range tree is also capable of 'bridging' gaps when adding
	+ * allocations. This is useful for cases when close proximity of
	+ * allocations is an important detail that needs to be represented
	+ * in the range tree. See range_tree_set_gap(). The default behavior
	+ * is not to bridge gaps (i.e. the maximum allowed gap size is 0).
	+ *
	+ * In order to traverse a range tree, use either the range_tree_walk()
	+ * or range_tree_vacate() functions.
	+ *
	+ * To obtain more accurate information on individual segment
	+ * operations that the range tree performs "under the hood", you can
	+ * specify a set of callbacks by passing a range_tree_ops_t structure
	+ * to the range_tree_create function. Any callbacks that are non-NULL
	+ * are then called at the appropriate times.
	+ *
	+ * The range tree code also supports a special variant of range trees
	+ * that can bridge small gaps between segments. This kind of tree is used
	+ * by the dsl scanning code to group I/Os into mostly sequential chunks to
	+ * optimize disk performance. The code here attempts to do this with as
	+ * little memory and computational overhead as possible. One limitation of
	+ * this implementation is that segments of range trees with gaps can only
	+ * support removing complete segments.
	+ */
	+
	kmem_cache_t *range_seg_cache;

	+/* Generic ops for managing an AVL tree alongside a range tree */
	+struct range_tree_ops rt_avl_ops = {
	+ .rtop_create = rt_avl_create,
	+ .rtop_destroy = rt_avl_destroy,
	+ .rtop_add = rt_avl_add,
	+ .rtop_remove = rt_avl_remove,
	+ .rtop_vacate = rt_avl_vacate,
	+};
	+
	void
	range_tree_init(void)
	{
	@@ -109,47 +159,47 @@
	static int
	range_tree_seg_compare(const void x1, const void x2)
	{
	- const range_seg_t *r1 = x1;
	- const range_seg_t *r2 = x2;
	+ const range_seg_t r1 = (const range_seg_t )x1;
	+ const range_seg_t r2 = (const range_seg_t )x2;

	- if (r1->rs_start < r2->rs_start) {
	- if (r1->rs_end > r2->rs_start)
	- return (0);
	- return (-1);
	- }
	- if (r1->rs_start > r2->rs_start) {
	- if (r1->rs_start < r2->rs_end)
	- return (0);
	- return (1);
	- }
	- return (0);
	+ ASSERT3U(r1->rs_start, <=, r1->rs_end);
	+ ASSERT3U(r2->rs_start, <=, r2->rs_end);
	+
	+ return ((r1->rs_start >= r2->rs_end) - (r1->rs_end <= r2->rs_start));
	}

	range_tree_t *
	-range_tree_create(range_tree_ops_t ops, void arg)
	+range_tree_create_impl(range_tree_ops_t ops, void arg,
	+ int (avl_compare) (const void , const void *), uint64_t gap)
	{
	- range_tree_t *rt;
	+ range_tree_t *rt = kmem_zalloc(sizeof (range_tree_t), KM_SLEEP);

	- rt = kmem_zalloc(sizeof (range_tree_t), KM_SLEEP);
	-
	avl_create(&rt->rt_root, range_tree_seg_compare,
	sizeof (range_seg_t), offsetof(range_seg_t, rs_node));

	rt->rt_ops = ops;
	rt->rt_arg = arg;
	+ rt->rt_gap = gap;
	+ rt->rt_avl_compare = avl_compare;

	- if (rt->rt_ops != NULL)
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_create != NULL)
	rt->rt_ops->rtop_create(rt, rt->rt_arg);

	return (rt);
	}

	+range_tree_t *
	+range_tree_create(range_tree_ops_t ops, void arg)
	+{
	+ return (range_tree_create_impl(ops, arg, NULL, 0));
	+}
	+
	void
	range_tree_destroy(range_tree_t *rt)
	{
	VERIFY0(rt->rt_space);

	- if (rt->rt_ops != NULL)
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_destroy != NULL)
	rt->rt_ops->rtop_destroy(rt, rt->rt_arg);

	avl_destroy(&rt->rt_root);
	@@ -157,39 +207,99 @@
	}

	void
	-range_tree_add(void *arg, uint64_t start, uint64_t size)
	+range_tree_adjust_fill(range_tree_t rt, range_seg_t rs, int64_t delta)
	{
	+ ASSERT3U(rs->rs_fill + delta, !=, 0);
	+ ASSERT3U(rs->rs_fill + delta, <=, rs->rs_end - rs->rs_start);
	+
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
	+ rt->rt_ops->rtop_remove(rt, rs, rt->rt_arg);
	+ rs->rs_fill += delta;
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_add != NULL)
	+ rt->rt_ops->rtop_add(rt, rs, rt->rt_arg);
	+}
	+
	+static void
	+range_tree_add_impl(void *arg, uint64_t start, uint64_t size, uint64_t fill)
	+{
	range_tree_t *rt = arg;
	avl_index_t where;
	range_seg_t rsearch, rs_before, rs_after, *rs;
	- uint64_t end = start + size;
	+ uint64_t end = start + size, gap = rt->rt_gap;
	+ uint64_t bridge_size = 0;
	boolean_t merge_before, merge_after;

	- VERIFY(size != 0);
	+ ASSERT3U(size, !=, 0);
	+ ASSERT3U(fill, <=, size);

	rsearch.rs_start = start;
	rsearch.rs_end = end;
	rs = avl_find(&rt->rt_root, &rsearch, &where);

	- if (rs != NULL && rs->rs_start <= start && rs->rs_end >= end) {
	+ if (gap == 0 && rs != NULL &&
	+ rs->rs_start <= start && rs->rs_end >= end) {
	zfs_panic_recover("zfs: allocating allocated segment"
	- "(offset=%llu size=%llu)\n",
	- (longlong_t)start, (longlong_t)size);
	+ "(offset=%llu size=%llu) of (offset=%llu size=%llu)\n",
	+ (longlong_t)start, (longlong_t)size,
	+ (longlong_t)rs->rs_start,
	+ (longlong_t)rs->rs_end - rs->rs_start);
	return;
	}

	- /* Make sure we don't overlap with either of our neighbors */
	- VERIFY(rs == NULL);
	+ /*
	+ * If this is a gap-supporting range tree, it is possible that we
	+ * are inserting into an existing segment. In this case simply
	+ * bump the fill count and call the remove / add callbacks. If the
	+ * new range will extend an existing segment, we remove the
	+ * existing one, apply the new extent to it and re-insert it using
	+ * the normal code paths.
	+ */
	+ if (rs != NULL) {
	+ ASSERT3U(gap, !=, 0);
	+ if (rs->rs_start <= start && rs->rs_end >= end) {
	+ range_tree_adjust_fill(rt, rs, fill);
	+ return;
	+ }

	+ avl_remove(&rt->rt_root, rs);
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
	+ rt->rt_ops->rtop_remove(rt, rs, rt->rt_arg);
	+
	+ range_tree_stat_decr(rt, rs);
	+ rt->rt_space -= rs->rs_end - rs->rs_start;
	+
	+ fill += rs->rs_fill;
	+ start = MIN(start, rs->rs_start);
	+ end = MAX(end, rs->rs_end);
	+ size = end - start;
	+
	+ range_tree_add_impl(rt, start, size, fill);
	+
	+ kmem_cache_free(range_seg_cache, rs);
	+ return;
	+ }
	+
	+ ASSERT3P(rs, ==, NULL);
	+
	+ /*
	+ * Determine whether or not we will have to merge with our neighbors.
	+ * If gap != 0, we might need to merge with our neighbors even if we
	+ * aren't directly touching.
	+ */
	rs_before = avl_nearest(&rt->rt_root, where, AVL_BEFORE);
	rs_after = avl_nearest(&rt->rt_root, where, AVL_AFTER);

	- merge_before = (rs_before != NULL && rs_before->rs_end == start);
	- merge_after = (rs_after != NULL && rs_after->rs_start == end);
	+ merge_before = (rs_before != NULL && rs_before->rs_end >= start - gap);
	+ merge_after = (rs_after != NULL && rs_after->rs_start <= end + gap);

	+ if (merge_before && gap != 0)
	+ bridge_size += start - rs_before->rs_end;
	+ if (merge_after && gap != 0)
	+ bridge_size += rs_after->rs_start - end;
	+
	if (merge_before && merge_after) {
	avl_remove(&rt->rt_root, rs_before);
	- if (rt->rt_ops != NULL) {
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL) {
	rt->rt_ops->rtop_remove(rt, rs_before, rt->rt_arg);
	rt->rt_ops->rtop_remove(rt, rs_after, rt->rt_arg);
	}
	@@ -197,43 +307,59 @@
	range_tree_stat_decr(rt, rs_before);
	range_tree_stat_decr(rt, rs_after);

	+ rs_after->rs_fill += rs_before->rs_fill + fill;
	rs_after->rs_start = rs_before->rs_start;
	kmem_cache_free(range_seg_cache, rs_before);
	rs = rs_after;
	} else if (merge_before) {
	- if (rt->rt_ops != NULL)
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
	rt->rt_ops->rtop_remove(rt, rs_before, rt->rt_arg);

	range_tree_stat_decr(rt, rs_before);

	+ rs_before->rs_fill += fill;
	rs_before->rs_end = end;
	rs = rs_before;
	} else if (merge_after) {
	- if (rt->rt_ops != NULL)
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
	rt->rt_ops->rtop_remove(rt, rs_after, rt->rt_arg);

	range_tree_stat_decr(rt, rs_after);

	+ rs_after->rs_fill += fill;
	rs_after->rs_start = start;
	rs = rs_after;
	} else {
	rs = kmem_cache_alloc(range_seg_cache, KM_SLEEP);
	+
	+ rs->rs_fill = fill;
	rs->rs_start = start;
	rs->rs_end = end;
	avl_insert(&rt->rt_root, rs, where);
	}

	- if (rt->rt_ops != NULL)
	+ if (gap != 0)
	+ ASSERT3U(rs->rs_fill, <=, rs->rs_end - rs->rs_start);
	+ else
	+ ASSERT3U(rs->rs_fill, ==, rs->rs_end - rs->rs_start);
	+
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_add != NULL)
	rt->rt_ops->rtop_add(rt, rs, rt->rt_arg);

	range_tree_stat_incr(rt, rs);
	- rt->rt_space += size;
	+ rt->rt_space += size + bridge_size;
	}

	void
	-range_tree_remove(void *arg, uint64_t start, uint64_t size)
	+range_tree_add(void *arg, uint64_t start, uint64_t size)
	{
	- range_tree_t *rt = arg;
	+ range_tree_add_impl(arg, start, size, size);
	+}
	+
	+static void
	+range_tree_remove_impl(range_tree_t *rt, uint64_t start, uint64_t size,
	+ boolean_t do_fill)
	+{
	avl_index_t where;
	range_seg_t rsearch, rs, newseg;
	uint64_t end = start + size;
	@@ -253,6 +379,34 @@
	(longlong_t)start, (longlong_t)size);
	return;
	}
	+
	+ /*
	+ * Range trees with gap support must only remove complete segments
	+ * from the tree. This allows us to maintain accurate fill accounting
	+ * and to ensure that bridged sections are not leaked. If we need to
	+ * remove less than the full segment, we can only adjust the fill count.
	+ */
	+ if (rt->rt_gap != 0) {
	+ if (do_fill) {
	+ if (rs->rs_fill == size) {
	+ start = rs->rs_start;
	+ end = rs->rs_end;
	+ size = end - start;
	+ } else {
	+ range_tree_adjust_fill(rt, rs, -size);
	+ return;
	+ }
	+ } else if (rs->rs_start != start \|\| rs->rs_end != end) {
	+ zfs_panic_recover("zfs: freeing partial segment of "
	+ "gap tree (offset=%llu size=%llu) of "
	+ "(offset=%llu size=%llu)",
	+ (longlong_t)start, (longlong_t)size,
	+ (longlong_t)rs->rs_start,
	+ (longlong_t)rs->rs_end - rs->rs_start);
	+ return;
	+ }
	+ }
	+
	VERIFY3U(rs->rs_start, <=, start);
	VERIFY3U(rs->rs_end, >=, end);

	@@ -261,19 +415,20 @@

	range_tree_stat_decr(rt, rs);

	- if (rt->rt_ops != NULL)
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
	rt->rt_ops->rtop_remove(rt, rs, rt->rt_arg);

	if (left_over && right_over) {
	newseg = kmem_cache_alloc(range_seg_cache, KM_SLEEP);
	newseg->rs_start = end;
	newseg->rs_end = rs->rs_end;
	+ newseg->rs_fill = newseg->rs_end - newseg->rs_start;
	range_tree_stat_incr(rt, newseg);

	rs->rs_end = start;

	avl_insert_here(&rt->rt_root, newseg, rs, AVL_AFTER);
	- if (rt->rt_ops != NULL)
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_add != NULL)
	rt->rt_ops->rtop_add(rt, newseg, rt->rt_arg);
	} else if (left_over) {
	rs->rs_end = start;
	@@ -286,15 +441,53 @@
	}

	if (rs != NULL) {
	+ /*
	+ * The fill of the leftover segment will always be equal to
	+ * the size, since we do not support removing partial segments
	+ * of range trees with gaps.
	+ */
	+ rs->rs_fill = rs->rs_end - rs->rs_start;
	range_tree_stat_incr(rt, rs);

	- if (rt->rt_ops != NULL)
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_add != NULL)
	rt->rt_ops->rtop_add(rt, rs, rt->rt_arg);
	}

	rt->rt_space -= size;
	}

	+void
	+range_tree_remove(void *arg, uint64_t start, uint64_t size)
	+{
	+ range_tree_remove_impl(arg, start, size, B_FALSE);
	+}
	+
	+void
	+range_tree_remove_fill(range_tree_t *rt, uint64_t start, uint64_t size)
	+{
	+ range_tree_remove_impl(rt, start, size, B_TRUE);
	+}
	+
	+void
	+range_tree_resize_segment(range_tree_t rt, range_seg_t rs,
	+ uint64_t newstart, uint64_t newsize)
	+{
	+ int64_t delta = newsize - (rs->rs_end - rs->rs_start);
	+
	+ range_tree_stat_decr(rt, rs);
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_remove != NULL)
	+ rt->rt_ops->rtop_remove(rt, rs, rt->rt_arg);
	+
	+ rs->rs_start = newstart;
	+ rs->rs_end = newstart + newsize;
	+
	+ range_tree_stat_incr(rt, rs);
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_add != NULL)
	+ rt->rt_ops->rtop_add(rt, rs, rt->rt_arg);
	+
	+ rt->rt_space += delta;
	+}
	+
	static range_seg_t *
	range_tree_find_impl(range_tree_t *rt, uint64_t start, uint64_t size)
	{
	@@ -309,7 +502,7 @@
	return (avl_find(&rt->rt_root, &rsearch, &where));
	}

	-static range_seg_t *
	+range_seg_t *
	range_tree_find(range_tree_t *rt, uint64_t start, uint64_t size)
	{
	range_seg_t *rs = range_tree_find_impl(rt, start, size);
	@@ -373,7 +566,7 @@
	void *cookie = NULL;


	- if (rt->rt_ops != NULL)
	+ if (rt->rt_ops != NULL && rt->rt_ops->rtop_vacate != NULL)
	rt->rt_ops->rtop_vacate(rt, rt->rt_arg);

	while ((rs = avl_destroy_nodes(&rt->rt_root, &cookie)) != NULL) {
	@@ -395,10 +588,61 @@
	func(arg, rs->rs_start, rs->rs_end - rs->rs_start);
	}

	+range_seg_t *
	+range_tree_first(range_tree_t *rt)
	+{
	+ return (avl_first(&rt->rt_root));
	+}
	+
	uint64_t
	range_tree_space(range_tree_t *rt)
	{
	return (rt->rt_space);
	+}
	+
	+/* Generic range tree functions for maintaining segments in an AVL tree. */
	+void
	+rt_avl_create(range_tree_t rt, void arg)
	+{
	+ avl_tree_t *tree = arg;
	+
	+ avl_create(tree, rt->rt_avl_compare, sizeof (range_seg_t),
	+ offsetof(range_seg_t, rs_pp_node));
	+}
	+
	+void
	+rt_avl_destroy(range_tree_t rt, void arg)
	+{
	+ avl_tree_t *tree = arg;
	+
	+ ASSERT0(avl_numnodes(tree));
	+ avl_destroy(tree);
	+}
	+
	+void
	+rt_avl_add(range_tree_t rt, range_seg_t rs, void *arg)
	+{
	+ avl_tree_t *tree = arg;
	+ avl_add(tree, rs);
	+}
	+
	+void
	+rt_avl_remove(range_tree_t rt, range_seg_t rs, void *arg)
	+{
	+ avl_tree_t *tree = arg;
	+ avl_remove(tree, rs);
	+}
	+
	+void
	+rt_avl_vacate(range_tree_t rt, void arg)
	+{
	+ /*
	+ * Normally one would walk the tree freeing nodes along the way.
	+ * Since the nodes are shared with the range trees we can avoid
	+ * walking all nodes and just reinitialize the avl tree. The nodes
	+ * will be freed by the range tree, so we don't want to free them here.
	+ */
	+ rt_avl_create(rt, arg);
	}

	boolean_t
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa.c
	@@ -2035,7 +2035,7 @@
	}

	mutex_enter(&spa->spa_scrub_lock);
	- spa->spa_scrub_inflight--;
	+ spa->spa_load_verify_ios--;
	cv_broadcast(&spa->spa_scrub_io_cv);
	mutex_exit(&spa->spa_scrub_lock);
	}
	@@ -2082,9 +2082,9 @@
	size_t size = BP_GET_PSIZE(bp);

	mutex_enter(&spa->spa_scrub_lock);
	- while (spa->spa_scrub_inflight >= spa_load_verify_maxinflight)
	+ while (spa->spa_load_verify_ios >= spa_load_verify_maxinflight)
	cv_wait(&spa->spa_scrub_io_cv, &spa->spa_scrub_lock);
	- spa->spa_scrub_inflight++;
	+ spa->spa_load_verify_ios++;
	mutex_exit(&spa->spa_scrub_lock);

	zio_nowait(zio_read(rio, spa, bp, abd_alloc_for_io(size, B_FALSE), size,
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_misc.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_misc.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/spa_misc.c
	@@ -2095,6 +2095,8 @@
	zpool_feature_init();
	spa_config_load();
	l2arc_start();
	+ scan_init();
	+ dsl_scan_global_init();
	#ifndef illumos
	#ifdef _KERNEL
	zfs_deadman_init();
	@@ -2119,7 +2121,8 @@
	range_tree_fini();
	unique_fini();
	refcount_fini();
	-
	+ scan_fini();
	+
	avl_destroy(&spa_namespace_avl);
	avl_destroy(&spa_spare_avl);
	avl_destroy(&spa_l2cache_avl);
	@@ -2220,6 +2223,7 @@
	spa->spa_scan_pass_scrub_pause = 0;
	spa->spa_scan_pass_scrub_spent_paused = 0;
	spa->spa_scan_pass_exam = 0;
	+ spa->spa_scan_pass_issued = 0;
	vdev_scan_stat_init(spa->spa_root_vdev);
	}

	@@ -2237,18 +2241,20 @@

	/* data stored on disk */
	ps->pss_func = scn->scn_phys.scn_func;
	+ ps->pss_state = scn->scn_phys.scn_state;
	ps->pss_start_time = scn->scn_phys.scn_start_time;
	ps->pss_end_time = scn->scn_phys.scn_end_time;
	ps->pss_to_examine = scn->scn_phys.scn_to_examine;
	- ps->pss_examined = scn->scn_phys.scn_examined;
	ps->pss_to_process = scn->scn_phys.scn_to_process;
	ps->pss_processed = scn->scn_phys.scn_processed;
	ps->pss_errors = scn->scn_phys.scn_errors;
	- ps->pss_state = scn->scn_phys.scn_state;
	-
	+ ps->pss_examined = scn->scn_phys.scn_examined;
	+ ps->pss_issued =
	+ scn->scn_issued_before_pass + spa->spa_scan_pass_issued;
	/* data not stored on disk */
	ps->pss_pass_start = spa->spa_scan_pass_start;
	ps->pss_pass_exam = spa->spa_scan_pass_exam;
	+ ps->pss_pass_issued = spa->spa_scan_pass_issued;
	ps->pss_pass_scrub_pause = spa->spa_scan_pass_scrub_pause;
	ps->pss_pass_scrub_spent_paused = spa->spa_scan_pass_scrub_spent_paused;

	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/arc.h
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/arc.h
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/arc.h
	@@ -58,11 +58,13 @@

	typedef struct arc_buf_hdr arc_buf_hdr_t;
	typedef struct arc_buf arc_buf_t;
	-typedef void arc_done_func_t(zio_t zio, arc_buf_t buf, void *priv);
	+typedef void arc_read_done_func_t(zio_t zio, const zbookmark_phys_t zb,
	+ const blkptr_t bp, arc_buf_t buf, void *priv);
	+typedef void arc_write_done_func_t(zio_t zio, arc_buf_t buf, void *priv);

	/* generic arc_done_func_t's which you can use */
	-arc_done_func_t arc_bcopy_func;
	-arc_done_func_t arc_getbuf_func;
	+arc_read_done_func_t arc_bcopy_func;
	+arc_read_done_func_t arc_getbuf_func;

	typedef enum arc_flags
	{
	@@ -75,35 +77,36 @@
	ARC_FLAG_CACHED = 1 << 3, /* I/O was in cache */
	ARC_FLAG_L2CACHE = 1 << 4, /* cache in L2ARC */
	ARC_FLAG_PREDICTIVE_PREFETCH = 1 << 5, /* I/O from zfetch */
	+ ARC_FLAG_PRESCIENT_PREFETCH = 1 << 6, /* long min lifespan */

	/*
	* Private ARC flags. These flags are private ARC only flags that
	* will show up in b_flags in the arc_hdr_buf_t. These flags should
	* only be set by ARC code.
	*/
	- ARC_FLAG_IN_HASH_TABLE = 1 << 6, /* buffer is hashed */
	- ARC_FLAG_IO_IN_PROGRESS = 1 << 7, /* I/O in progress */
	- ARC_FLAG_IO_ERROR = 1 << 8, /* I/O failed for buf */
	- ARC_FLAG_INDIRECT = 1 << 9, /* indirect block */
	+ ARC_FLAG_IN_HASH_TABLE = 1 << 7, /* buffer is hashed */
	+ ARC_FLAG_IO_IN_PROGRESS = 1 << 8, /* I/O in progress */
	+ ARC_FLAG_IO_ERROR = 1 << 9, /* I/O failed for buf */
	+ ARC_FLAG_INDIRECT = 1 << 10, /* indirect block */
	/* Indicates that block was read with ASYNC priority. */
	- ARC_FLAG_PRIO_ASYNC_READ = 1 << 10,
	- ARC_FLAG_L2_WRITING = 1 << 11, /* write in progress */
	- ARC_FLAG_L2_EVICTED = 1 << 12, /* evicted during I/O */
	- ARC_FLAG_L2_WRITE_HEAD = 1 << 13, /* head of write list */
	+ ARC_FLAG_PRIO_ASYNC_READ = 1 << 11,
	+ ARC_FLAG_L2_WRITING = 1 << 12, /* write in progress */
	+ ARC_FLAG_L2_EVICTED = 1 << 13, /* evicted during I/O */
	+ ARC_FLAG_L2_WRITE_HEAD = 1 << 14, /* head of write list */
	/* indicates that the buffer contains metadata (otherwise, data) */
	- ARC_FLAG_BUFC_METADATA = 1 << 14,
	+ ARC_FLAG_BUFC_METADATA = 1 << 15,

	/* Flags specifying whether optional hdr struct fields are defined */
	- ARC_FLAG_HAS_L1HDR = 1 << 15,
	- ARC_FLAG_HAS_L2HDR = 1 << 16,
	+ ARC_FLAG_HAS_L1HDR = 1 << 16,
	+ ARC_FLAG_HAS_L2HDR = 1 << 17,

	/*
	* Indicates the arc_buf_hdr_t's b_pdata matches the on-disk data.
	* This allows the l2arc to use the blkptr's checksum to verify
	* the data without having to store the checksum in the hdr.
	*/
	- ARC_FLAG_COMPRESSED_ARC = 1 << 17,
	- ARC_FLAG_SHARED_DATA = 1 << 18,
	+ ARC_FLAG_COMPRESSED_ARC = 1 << 18,
	+ ARC_FLAG_SHARED_DATA = 1 << 19,

	/*
	* The arc buffer's compression mode is stored in the top 7 bits of the
	@@ -179,12 +182,12 @@
	#endif

	int arc_read(zio_t pio, spa_t spa, const blkptr_t *bp,
	- arc_done_func_t done, void priv, zio_priority_t priority, int flags,
	- arc_flags_t arc_flags, const zbookmark_phys_t zb);
	+ arc_read_done_func_t done, void priv, zio_priority_t priority,
	+ int flags, arc_flags_t arc_flags, const zbookmark_phys_t zb);
	zio_t arc_write(zio_t pio, spa_t *spa, uint64_t txg,
	blkptr_t bp, arc_buf_t buf, boolean_t l2arc, const zio_prop_t *zp,
	- arc_done_func_t ready, arc_done_func_t child_ready,
	- arc_done_func_t physdone, arc_done_func_t done,
	+ arc_write_done_func_t ready, arc_write_done_func_t child_ready,
	+ arc_write_done_func_t physdone, arc_write_done_func_t done,
	void *priv, zio_priority_t priority, int zio_flags,
	const zbookmark_phys_t *zb);
	void arc_freed(spa_t spa, const blkptr_t bp);
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_pool.h
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_pool.h
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_pool.h
	@@ -76,6 +76,7 @@

	typedef struct zfs_all_blkstats {
	zfs_blkstat_t zab_type[DN_MAX_LEVELS + 1][DMU_OT_TOTAL + 1];
	+ kmutex_t zab_lock;
	} zfs_all_blkstats_t;


	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_scan.h
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_scan.h
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_scan.h
	@@ -107,24 +107,58 @@
	typedef struct dsl_scan {
	struct dsl_pool *scn_dp;

	- boolean_t scn_suspending;
	uint64_t scn_restart_txg;
	uint64_t scn_done_txg;
	uint64_t scn_sync_start_time;
	- zio_t *scn_zio_root;
	+ uint64_t scn_issued_before_pass;

	/* for freeing blocks */
	boolean_t scn_is_bptree;
	boolean_t scn_async_destroying;
	boolean_t scn_async_stalled;
	uint64_t scn_async_block_min_time_ms;
	+ /* flags and stats for controlling scan state */
	+ boolean_t scn_is_sorted; /* doing sequential scan */
	+ boolean_t scn_clearing; /* scan is issuing sequential extents */
	+ boolean_t scn_checkpointing; /* scan is issuing all queued extents */
	+ boolean_t scn_suspending; /* scan is suspending until next txg */
	+ uint64_t scn_last_checkpoint; /* time of last checkpoint */

	- /* for debugging / information */
	- uint64_t scn_visited_this_txg;
	+ /* members for thread synchronization */
	+ zio_t scn_zio_root; / root zio for waiting on IO */
	+ taskq_t scn_taskq; / task queue for issuing extents */

	- dsl_scan_phys_t scn_phys;
	+ /* for controlling scan prefetch, protected by spa_scrub_lock */
	+ boolean_t scn_prefetch_stop; /* prefetch should stop */
	+ zbookmark_phys_t scn_prefetch_bookmark; /* prefetch start bookmark */
	+ avl_tree_t scn_prefetch_queue; /* priority queue of prefetch IOs */
	+ uint64_t scn_maxinflight_bytes; /* max bytes in flight for poool */
	+
	+ /* per txg statistics */
	+ uint64_t scn_visited_this_txg; /* total bps visited this txg */
	+ uint64_t scn_holes_this_txg;
	+ uint64_t scn_lt_min_this_txg;
	+ uint64_t scn_gt_max_this_txg;
	+ uint64_t scn_ddt_contained_this_txg;
	+ uint64_t scn_objsets_visited_this_txg;
	+ uint64_t scn_avg_seg_size_this_txg;
	+ uint64_t scn_segs_this_txg;
	+ uint64_t scn_avg_zio_size_this_txg;
	+ uint64_t scn_zios_this_txg;
	+
	+ /* members needed for syncing scan status to disk */
	+ dsl_scan_phys_t scn_phys; /* on disk representation of scan */
	+ dsl_scan_phys_t scn_phys_cached;
	+ avl_tree_t scn_queue; /* queue of datasets to scan */
	+ uint64_t scn_bytes_pending; /* outstanding data to issue */
	} dsl_scan_t;

	+typedef struct dsl_scan_io_queue dsl_scan_io_queue_t;
	+
	+void dsl_scan_global_init(void);
	+
	+void scan_init(void);
	+void scan_fini(void);
	int dsl_scan_init(struct dsl_pool *dp, uint64_t txg);
	void dsl_scan_fini(struct dsl_pool *dp);
	void dsl_scan_sync(struct dsl_pool , dmu_tx_t );
	@@ -143,6 +177,9 @@
	struct dmu_tx *tx);
	boolean_t dsl_scan_active(dsl_scan_t *scn);
	boolean_t dsl_scan_is_paused_scrub(const dsl_scan_t *scn);
	+void dsl_scan_freed(spa_t spa, const blkptr_t bp);
	+void dsl_scan_io_queue_destroy(dsl_scan_io_queue_t *queue);
	+void dsl_scan_io_queue_vdev_xfer(vdev_t svd, vdev_t tvd);

	#ifdef __cplusplus
	}
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/range_tree.h
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/range_tree.h
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/range_tree.h
	@@ -51,6 +51,9 @@
	range_tree_ops_t *rt_ops;
	void *rt_arg;

	+ /* rt_avl_compare should only be set it rt_arg is an AVL tree */
	+ uint64_t rt_gap; /* allowable inter-segment gap */
	+ int (rt_avl_compare)(const void , const void *);
	/*
	* The rt_histogram maintains a histogram of ranges. Each bucket,
	* rt_histogram[i], contains the number of ranges whose size is:
	@@ -64,6 +67,7 @@
	avl_node_t rs_pp_node; /* AVL picker-private node */
	uint64_t rs_start; /* starting offset of this segment */
	uint64_t rs_end; /* ending offset (non-inclusive) */
	+ uint64_t rs_fill; /* actual fill if gap mode is on */
	} range_seg_t;

	struct range_tree_ops {
	@@ -78,9 +82,14 @@

	void range_tree_init(void);
	void range_tree_fini(void);
	-range_tree_t range_tree_create(range_tree_ops_t ops, void *arg);
	+range_tree_t range_tree_create_impl(range_tree_ops_t ops, void *arg,
	+ int (avl_compare)(const void, const void*), uint64_t gap);
	+ range_tree_t range_tree_create(range_tree_ops_t ops, void *arg);
	void range_tree_destroy(range_tree_t *rt);
	boolean_t range_tree_contains(range_tree_t *rt, uint64_t start, uint64_t size);
	+range_seg_t range_tree_find(range_tree_t rt, uint64_t start, uint64_t size);
	+void range_tree_resize_segment(range_tree_t rt, range_seg_t rs,
	+ uint64_t newstart, uint64_t newsize);
	uint64_t range_tree_space(range_tree_t *rt);
	boolean_t range_tree_is_empty(range_tree_t *rt);
	void range_tree_verify(range_tree_t *rt, uint64_t start, uint64_t size);
	@@ -89,10 +98,27 @@

	void range_tree_add(void *arg, uint64_t start, uint64_t size);
	void range_tree_remove(void *arg, uint64_t start, uint64_t size);
	+void range_tree_remove_fill(range_tree_t *rt, uint64_t start, uint64_t size);
	+void range_tree_adjust_fill(range_tree_t rt, range_seg_t rs, int64_t delta);
	void range_tree_clear(range_tree_t *rt, uint64_t start, uint64_t size);

	void range_tree_vacate(range_tree_t rt, range_tree_func_t func, void *arg);
	void range_tree_walk(range_tree_t rt, range_tree_func_t func, void *arg);
	+range_seg_t range_tree_first(range_tree_t rt);
	+
	+void rt_avl_create(range_tree_t rt, void arg);
	+void rt_avl_destroy(range_tree_t rt, void arg);
	+void rt_avl_add(range_tree_t rt, range_seg_t rs, void *arg);
	+void rt_avl_remove(range_tree_t rt, range_seg_t rs, void *arg);
	+void rt_avl_vacate(range_tree_t rt, void arg);
	+extern struct range_tree_ops rt_avl_ops;
	+
	+void rt_avl_create(range_tree_t rt, void arg);
	+void rt_avl_destroy(range_tree_t rt, void arg);
	+void rt_avl_add(range_tree_t rt, range_seg_t rs, void *arg);
	+void rt_avl_remove(range_tree_t rt, range_seg_t rs, void *arg);
	+void rt_avl_vacate(range_tree_t rt, void arg);
	+extern struct range_tree_ops rt_avl_ops;

	#ifdef __cplusplus
	}
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa_impl.h
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa_impl.h
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/spa_impl.h
	@@ -257,7 +257,8 @@
	boolean_t spa_extreme_rewind; /* rewind past deferred frees */
	uint64_t spa_last_io; /* lbolt of last non-scan I/O */
	kmutex_t spa_scrub_lock; /* resilver/scrub lock */
	- uint64_t spa_scrub_inflight; /* in-flight scrub I/Os */
	+ uint64_t spa_scrub_inflight; /* in-flight scrub bytes */
	+ uint64_t spa_load_verify_ios; /* in-flight verifications IOs */
	kcondvar_t spa_scrub_io_cv; /* scrub I/O completion */
	uint8_t spa_scrub_active; /* active or suspended? */
	uint8_t spa_scrub_type; /* type of scrub we're doing */
	@@ -268,6 +269,7 @@
	uint64_t spa_scan_pass_scrub_pause; /* scrub pause time */
	uint64_t spa_scan_pass_scrub_spent_paused; /* total paused */
	uint64_t spa_scan_pass_exam; /* examined bytes per pass */
	+ uint64_t spa_scan_pass_issued; /* issued bytes per pass */
	kmutex_t spa_async_lock; /* protect async state */
	kthread_t spa_async_thread; / thread doing async task */
	kthread_t spa_async_thread_vd; / thread doing vd async task */
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/vdev.h
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/vdev.h
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/vdev.h
	@@ -71,6 +71,7 @@
	extern boolean_t vdev_dtl_contains(vdev_t *vd, vdev_dtl_type_t d,
	uint64_t txg, uint64_t size);
	extern boolean_t vdev_dtl_empty(vdev_t *vd, vdev_dtl_type_t d);
	+extern boolean_t vdev_dtl_need_resilver(vdev_t *vd, uint64_t off, size_t size);
	extern void vdev_dtl_reassess(vdev_t *vd, uint64_t txg, uint64_t scrub_txg,
	int scrub_done);
	extern boolean_t vdev_dtl_required(vdev_t *vd);
	@@ -135,6 +136,7 @@
	extern void vdev_queue_fini(vdev_t *vd);
	extern zio_t vdev_queue_io(zio_t zio);
	extern void vdev_queue_io_done(zio_t *zio);
	+extern void vdev_queue_change_io_priority(zio_t *zio, zio_priority_t priority);
	extern int vdev_queue_length(vdev_t *vd);
	extern uint64_t vdev_queue_lastoffset(vdev_t *vd);
	extern void vdev_queue_register_lastoffset(vdev_t vd, zio_t zio);
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/vdev_impl.h
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/vdev_impl.h
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/vdev_impl.h
	@@ -71,6 +71,7 @@
	typedef void vdev_io_start_func_t(zio_t *zio);
	typedef void vdev_io_done_func_t(zio_t *zio);
	typedef void vdev_state_change_func_t(vdev_t *vd, int, int);
	+typedef boolean_t vdev_need_resilver_func_t(vdev_t *vd, uint64_t, size_t);
	typedef void vdev_hold_func_t(vdev_t *vd);
	typedef void vdev_rele_func_t(vdev_t *vd);

	@@ -86,6 +87,7 @@
	vdev_io_start_func_t *vdev_op_io_start;
	vdev_io_done_func_t *vdev_op_io_done;
	vdev_state_change_func_t *vdev_op_state_change;
	+ vdev_need_resilver_func_t *vdev_op_need_resilver;
	vdev_hold_func_t *vdev_op_hold;
	vdev_rele_func_t *vdev_op_rele;
	vdev_remap_func_t *vdev_op_remap;
	@@ -293,6 +295,13 @@
	*/
	uint64_t vdev_async_write_queue_depth;
	uint64_t vdev_max_async_write_queue_depth;
	+
	+ /*
	+ * Protects the vdev_scan_io_queue field itself as well as the
	+ * structure's contents (when present).
	+ */
	+ kmutex_t vdev_scan_io_queue_lock;
	+ struct dsl_scan_io_queue *vdev_scan_io_queue;

	/*
	* Leaf vdev state.
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zio.h
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zio.h
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zio.h
	@@ -593,6 +593,8 @@
	extern void zio_vdev_io_reissue(zio_t *zio);
	extern void zio_vdev_io_redone(zio_t *zio);

	+extern void zio_change_priority(zio_t *pio, zio_priority_t priority);
	+
	extern void zio_checksum_verified(zio_t *zio);
	extern int zio_worst_error(int e1, int e2);

	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev.c
	@@ -559,6 +559,8 @@
	mutex_init(&vd->vdev_stat_lock, NULL, MUTEX_DEFAULT, NULL);
	mutex_init(&vd->vdev_probe_lock, NULL, MUTEX_DEFAULT, NULL);
	mutex_init(&vd->vdev_queue_lock, NULL, MUTEX_DEFAULT, NULL);
	+ mutex_init(&vd->vdev_scan_io_queue_lock, NULL, MUTEX_DEFAULT, NULL);
	+
	for (int t = 0; t < DTL_TYPES; t++) {
	vd->vdev_dtl[t] = range_tree_create(NULL, NULL);
	}
	@@ -832,6 +834,18 @@
	spa_t *spa = vd->vdev_spa;

	/*
	+ * Scan queues are normally destroyed at the end of a scan. If the
	+ * queue exists here, that implies the vdev is being removed while
	+ * the scan is still running.
	+ */
	+ if (vd->vdev_scan_io_queue != NULL) {
	+ mutex_enter(&vd->vdev_scan_io_queue_lock);
	+ dsl_scan_io_queue_destroy(vd->vdev_scan_io_queue);
	+ vd->vdev_scan_io_queue = NULL;
	+ mutex_exit(&vd->vdev_scan_io_queue_lock);
	+ }
	+
	+ /*
	* vdev_free() implies closing the vdev first. This is simpler than
	* trying to ensure complicated semantics for all callers.
	*/
	@@ -920,6 +934,7 @@
	mutex_destroy(&vd->vdev_dtl_lock);
	mutex_destroy(&vd->vdev_stat_lock);
	mutex_destroy(&vd->vdev_probe_lock);
	+ mutex_destroy(&vd->vdev_scan_io_queue_lock);

	if (vd == spa->spa_root_vdev)
	spa->spa_root_vdev = NULL;
	@@ -996,6 +1011,8 @@

	tvd->vdev_islog = svd->vdev_islog;
	svd->vdev_islog = 0;
	+
	+ dsl_scan_io_queue_vdev_xfer(svd, tvd);
	}

	static void
	@@ -2286,6 +2303,21 @@
	mutex_exit(&vd->vdev_dtl_lock);

	return (empty);
	+}
	+
	+/*
	+ * Returns B_TRUE if vdev determines offset needs to be resilvered.
	+ */
	+boolean_t
	+vdev_dtl_need_resilver(vdev_t *vd, uint64_t offset, size_t psize)
	+{
	+ ASSERT(vd != vd->vdev_spa->spa_root_vdev);
	+
	+ if (vd->vdev_ops->vdev_op_need_resilver == NULL \|\|
	+ vd->vdev_ops->vdev_op_leaf)
	+ return (B_TRUE);
	+
	+ return (vd->vdev_ops->vdev_op_need_resilver(vd, offset, psize));
	}

	/*
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_disk.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_disk.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_disk.c
	@@ -837,6 +837,7 @@
	vdev_disk_io_start,
	vdev_disk_io_done,
	NULL,
	+ NULL,
	vdev_disk_hold,
	vdev_disk_rele,
	NULL,
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_file.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_file.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_file.c
	@@ -267,6 +267,7 @@
	vdev_file_io_start,
	vdev_file_io_done,
	NULL,
	+ NULL,
	vdev_file_hold,
	vdev_file_rele,
	NULL,
	@@ -285,6 +286,7 @@
	vdev_default_asize,
	vdev_file_io_start,
	vdev_file_io_done,
	+ NULL,
	NULL,
	vdev_file_hold,
	vdev_file_rele,
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
	@@ -1147,6 +1147,7 @@
	vdev_geom_io_start,
	vdev_geom_io_done,
	NULL,
	+ NULL,
	vdev_geom_hold,
	vdev_geom_rele,
	NULL,
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_indirect.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_indirect.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_indirect.c
	@@ -1111,6 +1111,7 @@
	NULL,
	NULL,
	NULL,
	+ NULL,
	vdev_indirect_remap,
	VDEV_TYPE_INDIRECT, /* name of this vdev type */
	B_FALSE /* leaf vdev */
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_mirror.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_mirror.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_mirror.c
	@@ -722,6 +722,7 @@
	NULL,
	NULL,
	NULL,
	+ NULL,
	VDEV_TYPE_MIRROR, /* name of this vdev type */
	B_FALSE /* not a leaf vdev */
	};
	@@ -736,6 +737,7 @@
	NULL,
	NULL,
	NULL,
	+ NULL,
	VDEV_TYPE_REPLACING, /* name of this vdev type */
	B_FALSE /* not a leaf vdev */
	};
	@@ -747,6 +749,7 @@
	vdev_mirror_io_start,
	vdev_mirror_io_done,
	vdev_mirror_state_change,
	+ NULL,
	NULL,
	NULL,
	NULL,
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_missing.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_missing.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_missing.c
	@@ -90,6 +90,7 @@
	NULL,
	NULL,
	NULL,
	+ NULL,
	VDEV_TYPE_MISSING, /* name of this vdev type */
	B_TRUE /* leaf vdev */
	};
	@@ -100,6 +101,7 @@
	vdev_default_asize,
	vdev_missing_io_start,
	vdev_missing_io_done,
	+ NULL,
	NULL,
	NULL,
	NULL,
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_queue.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_queue.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_queue.c
	@@ -175,7 +175,7 @@
	* we include spans of optional I/Os to aid aggregation at the disk even when
	* they aren't able to help us aggregate at this level.
	*/
	-int zfs_vdev_aggregation_limit = SPA_OLD_MAXBLOCKSIZE;
	+int zfs_vdev_aggregation_limit = 1 << 20;
	int zfs_vdev_read_gap_limit = 32 << 10;
	int zfs_vdev_write_gap_limit = 4 << 10;

	@@ -933,6 +933,48 @@
	zio_execute(nio);
	}
	mutex_enter(&vq->vq_lock);
	+ }
	+
	+ mutex_exit(&vq->vq_lock);
	+}
	+
	+void
	+vdev_queue_change_io_priority(zio_t *zio, zio_priority_t priority)
	+{
	+ vdev_queue_t *vq = &zio->io_vd->vdev_queue;
	+ avl_tree_t *tree;
	+
	+ ASSERT3U(zio->io_priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
	+ ASSERT3U(priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
	+
	+ if (zio->io_type == ZIO_TYPE_READ) {
	+ if (priority != ZIO_PRIORITY_SYNC_READ &&
	+ priority != ZIO_PRIORITY_ASYNC_READ &&
	+ priority != ZIO_PRIORITY_SCRUB)
	+ priority = ZIO_PRIORITY_ASYNC_READ;
	+ } else {
	+ ASSERT(zio->io_type == ZIO_TYPE_WRITE);
	+ if (priority != ZIO_PRIORITY_SYNC_WRITE &&
	+ priority != ZIO_PRIORITY_ASYNC_WRITE)
	+ priority = ZIO_PRIORITY_ASYNC_WRITE;
	+ }
	+
	+ mutex_enter(&vq->vq_lock);
	+
	+ /*
	+ * If the zio is in none of the queues we can simply change
	+ * the priority. If the zio is waiting to be submitted we must
	+ * remove it from the queue and re-insert it with the new priority.
	+ * Otherwise, the zio is currently active and we cannot change its
	+ * priority.
	+ */
	+ tree = vdev_queue_class_tree(vq, zio->io_priority);
	+ if (avl_find(tree, zio, NULL) == zio) {
	+ avl_remove(vdev_queue_class_tree(vq, zio->io_priority), zio);
	+ zio->io_priority = priority;
	+ avl_add(vdev_queue_class_tree(vq, zio->io_priority), zio);
	+ } else if (avl_find(&vq->vq_active_tree, zio, NULL) != zio) {
	+ zio->io_priority = priority;
	}

	mutex_exit(&vq->vq_lock);
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_raidz.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_raidz.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_raidz.c
	@@ -2584,6 +2584,44 @@
	vdev_set_state(vd, B_FALSE, VDEV_STATE_HEALTHY, VDEV_AUX_NONE);
	}

	+/*
	+ * Determine if any portion of the provided block resides on a child vdev
	+ * with a dirty DTL and therefore needs to be resilvered. The function
	+ * assumes that at least one DTL is dirty which imples that full stripe
	+ * width blocks must be resilvered.
	+ */
	+static boolean_t
	+vdev_raidz_need_resilver(vdev_t *vd, uint64_t offset, size_t psize)
	+{
	+ uint64_t dcols = vd->vdev_children;
	+ uint64_t nparity = vd->vdev_nparity;
	+ uint64_t ashift = vd->vdev_top->vdev_ashift;
	+ /* The starting RAIDZ (parent) vdev sector of the block. */
	+ uint64_t b = offset >> ashift;
	+ /* The zio's size in units of the vdev's minimum sector size. */
	+ uint64_t s = ((psize - 1) >> ashift) + 1;
	+ /* The first column for this stripe. */
	+ uint64_t f = b % dcols;
	+
	+ if (s + nparity >= dcols)
	+ return (B_TRUE);
	+
	+ for (uint64_t c = 0; c < s + nparity; c++) {
	+ uint64_t devidx = (f + c) % dcols;
	+ vdev_t *cvd = vd->vdev_child[devidx];
	+
	+ /*
	+ * dsl_scan_need_resilver() already checked vd with
	+ * vdev_dtl_contains(). So here just check cvd with
	+ * vdev_dtl_empty(), cheaper and a good approximation.
	+ */
	+ if (!vdev_dtl_empty(cvd, DTL_PARTIAL))
	+ return (B_TRUE);
	+ }
	+
	+ return (B_FALSE);
	+}
	+
	vdev_ops_t vdev_raidz_ops = {
	vdev_raidz_open,
	vdev_raidz_close,
	@@ -2591,6 +2629,7 @@
	vdev_raidz_io_start,
	vdev_raidz_io_done,
	vdev_raidz_state_change,
	+ vdev_raidz_need_resilver,
	NULL,
	NULL,
	NULL,
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_root.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_root.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_root.c
	@@ -150,6 +150,7 @@
	NULL,
	NULL,
	NULL,
	+ NULL,
	VDEV_TYPE_ROOT, /* name of this vdev type */
	B_FALSE /* not a leaf vdev */
	};
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zap.c
	@@ -1051,7 +1051,7 @@
	}
	err = zap_add(os, intoobj, za.za_name,
	8, 1, &value, tx);
	- if (err)
	+ if (err != 0)
	break;
	}
	zap_cursor_fini(&zc);
	Index: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zio.c
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zio.c
	+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zio.c
	@@ -41,6 +41,7 @@
	#include <sys/trim_map.h>
	#include <sys/blkptr.h>
	#include <sys/zfeature.h>
	+#include <sys/dsl_scan.h>
	#include <sys/metaslab_impl.h>
	#include <sys/abd.h>

	@@ -438,6 +439,8 @@
	{
	list_t *cl = &pio->io_child_list;

	+ ASSERT(MUTEX_HELD(&pio->io_lock));
	+
	zl = (zl == NULL) ? list_head(cl) : list_next(cl, *zl);
	if (*zl == NULL)
	return (NULL);
	@@ -472,8 +475,8 @@
	zl->zl_parent = pio;
	zl->zl_child = cio;

	- mutex_enter(&cio->io_lock);
	mutex_enter(&pio->io_lock);
	+ mutex_enter(&cio->io_lock);

	ASSERT(pio->io_state[ZIO_WAIT_DONE] == 0);

	@@ -486,8 +489,8 @@
	pio->io_child_count++;
	cio->io_parent_count++;

	- mutex_exit(&pio->io_lock);
	mutex_exit(&cio->io_lock);
	+ mutex_exit(&pio->io_lock);
	}

	static void
	@@ -496,8 +499,8 @@
	ASSERT(zl->zl_parent == pio);
	ASSERT(zl->zl_child == cio);

	- mutex_enter(&cio->io_lock);
	mutex_enter(&pio->io_lock);
	+ mutex_enter(&cio->io_lock);

	list_remove(&pio->io_child_list, zl);
	list_remove(&cio->io_parent_list, zl);
	@@ -505,9 +508,8 @@
	pio->io_child_count--;
	cio->io_parent_count--;

	- mutex_exit(&pio->io_lock);
	mutex_exit(&cio->io_lock);
	-
	+ mutex_exit(&pio->io_lock);
	kmem_cache_free(zio_link_cache, zl);
	}

	@@ -988,6 +990,7 @@

	metaslab_check_free(spa, bp);
	arc_freed(spa, bp);
	+ dsl_scan_freed(spa, bp);

	if (zfs_trim_enabled)
	stage \|= ZIO_STAGE_ISSUE_ASYNC \| ZIO_STAGE_VDEV_IO_START \|
	@@ -1865,14 +1868,16 @@
	* cannot be affected by any side effects of reexecuting 'cio'.
	*/
	zio_link_t *zl = NULL;
	+ mutex_enter(&pio->io_lock);
	for (cio = zio_walk_children(pio, &zl); cio != NULL; cio = cio_next) {
	cio_next = zio_walk_children(pio, &zl);
	- mutex_enter(&pio->io_lock);
	for (int w = 0; w < ZIO_WAIT_TYPES; w++)
	pio->io_children[cio->io_child_type][w]++;
	mutex_exit(&pio->io_lock);
	zio_reexecute(cio);
	+ mutex_enter(&pio->io_lock);
	}
	+ mutex_exit(&pio->io_lock);

	/*
	* Now that all children have been reexecuted, execute the parent.
	@@ -3184,26 +3189,25 @@
	}
	}

	- /*
	- * We keep track of time-sensitive I/Os so that the scan thread
	- * can quickly react to certain workloads. In particular, we care
	- * about non-scrubbing, top-level reads and writes with the following
	- * characteristics:
	- * - synchronous writes of user data to non-slog devices
	- * - any reads of user data
	- * When these conditions are met, adjust the timestamp of spa_last_io
	- * which allows the scan thread to adjust its workload accordingly.
	- */
	- if (!(zio->io_flags & ZIO_FLAG_SCAN_THREAD) && zio->io_bp != NULL &&
	- vd == vd->vdev_top && !vd->vdev_islog &&
	- zio->io_bookmark.zb_objset != DMU_META_OBJSET &&
	- zio->io_txg != spa_syncing_txg(spa)) {
	- uint64_t old = spa->spa_last_io;
	- uint64_t new = ddi_get_lbolt64();
	- if (old != new)
	- (void) atomic_cas_64(&spa->spa_last_io, old, new);
	- }
	-
	+ /*
	+ * We keep track of time-sensitive I/Os so that the scan thread
	+ * can quickly react to certain workloads. In particular, we care
	+ * about non-scrubbing, top-level reads and writes with the following
	+ * characteristics:
	+ * - synchronous writes of user data to non-slog devices
	+ * - any reads of user data
	+ * When these conditions are met, adjust the timestamp of spa_last_io
	+ * which allows the scan thread to adjust its workload accordingly.
	+ */
	+ if (!(zio->io_flags & ZIO_FLAG_SCAN_THREAD) && zio->io_bp != NULL &&
	+ vd == vd->vdev_top && !vd->vdev_islog &&
	+ zio->io_bookmark.zb_objset != DMU_META_OBJSET &&
	+ zio->io_txg != spa_syncing_txg(spa)) {
	+ uint64_t old = spa->spa_last_io;
	+ uint64_t new = ddi_get_lbolt64();
	+ if (old != new)
	+ (void) atomic_cas_64(&spa->spa_last_io, old, new);
	+ }
	align = 1ULL << vd->vdev_top->vdev_ashift;

	if (!(zio->io_flags & ZIO_FLAG_PHYSICAL) &&
	@@ -3350,6 +3354,35 @@
	VERIFY(vdev_probe(vd, zio) == NULL);

	return (ZIO_PIPELINE_CONTINUE);
	+}
	+
	+/*
	+ * This function is used to change the priority of an existing zio that is
	+ * currently in-flight. This is used by the arc to upgrade priority in the
	+ * event that a demand read is made for a block that is currently queued
	+ * as a scrub or async read IO. Otherwise, the high priority read request
	+ * would end up having to wait for the lower priority IO.
	+ */
	+void
	+zio_change_priority(zio_t *pio, zio_priority_t priority)
	+{
	+ zio_t cio, cio_next;
	+ zio_link_t *zl = NULL;
	+
	+ ASSERT3U(priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
	+
	+ if (pio->io_vd != NULL && pio->io_vd->vdev_ops->vdev_op_leaf) {
	+ vdev_queue_change_io_priority(pio, priority);
	+ } else {
	+ pio->io_priority = priority;
	+ }
	+
	+ mutex_enter(&pio->io_lock);
	+ for (cio = zio_walk_children(pio, &zl); cio != NULL; cio = cio_next) {
	+ cio_next = zio_walk_children(pio, &zl);
	+ zio_change_priority(cio, priority);
	+ }
	+ mutex_exit(&pio->io_lock);
	}

	/*
	Index: head/sys/cddl/contrib/opensolaris/uts/common/sys/fs/zfs.h
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/sys/fs/zfs.h
	+++ head/sys/cddl/contrib/opensolaris/uts/common/sys/fs/zfs.h
	@@ -760,7 +760,7 @@
	uint64_t pss_start_time; /* scan start time */
	uint64_t pss_end_time; /* scan end time */
	uint64_t pss_to_examine; /* total bytes to scan */
	- uint64_t pss_examined; /* total examined bytes */
	+ uint64_t pss_examined; /* total bytes located by scanner */
	uint64_t pss_to_process; /* total bytes to process */
	uint64_t pss_processed; /* total processed bytes */
	uint64_t pss_errors; /* scan errors */
	@@ -771,6 +771,12 @@
	uint64_t pss_pass_scrub_pause; /* pause time of a scurb pass */
	/* cumulative time scrub spent paused, needed for rate calculation */
	uint64_t pss_pass_scrub_spent_paused;
	+
	+ /* Sorted scrubbing new fields */
	+ /* Stored on disk */
	+ uint64_t pss_issued; /* total bytes checked by scanner */
	+ /* Not stored on disk */
	+ uint64_t pss_pass_issued; /* issued bytes per scan pass */
	} pool_scan_stat_t;

	typedef struct pool_removal_stat {
	Index: head/sys/cddl/contrib/opensolaris/uts/common/sys/taskq.h
	===================================================================
	--- head/sys/cddl/contrib/opensolaris/uts/common/sys/taskq.h
	+++ head/sys/cddl/contrib/opensolaris/uts/common/sys/taskq.h
	@@ -72,6 +72,8 @@
	#define TQ_NOALLOC 0x04 /* cannot allocate memory; may fail */
	#define TQ_FRONT 0x08 /* Put task at the front of the queue */

	+#define TASKQID_INVALID ((taskqid_t)0)
	+
	#ifdef _KERNEL

	extern taskq_t *system_taskq;
	@@ -91,6 +93,7 @@
	void nulltask(void *);
	void taskq_destroy(taskq_t *);
	void taskq_wait(taskq_t *);
	+void taskq_wait_id(taskq_t *, taskqid_t);
	void taskq_suspend(taskq_t *);
	int taskq_suspended(taskq_t *);
	void taskq_resume(taskq_t *);

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