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Index: head/sys/kern/kern_sendfile.c
===================================================================
--- head/sys/kern/kern_sendfile.c
+++ head/sys/kern/kern_sendfile.c
@@ -128,6 +128,7 @@
static void
sendfile_free_page(vm_page_t pg, bool nocache)
{
+ bool freed;
vm_page_lock(pg);
/*
@@ -136,15 +137,15 @@
* responsible for freeing the page. In 'noncache' case try to free
* the page, but only if it is cheap to.
*/
- if (vm_page_unwire(pg, nocache ? PQ_NONE : PQ_INACTIVE)) {
+ if (vm_page_unwire_noq(pg)) {
vm_object_t obj;
if ((obj = pg->object) == NULL)
vm_page_free(pg);
- else if (nocache) {
- if (!vm_page_xbusied(pg) && VM_OBJECT_TRYWLOCK(obj)) {
- bool freed;
-
+ else {
+ freed = false;
+ if (nocache && !vm_page_xbusied(pg) &&
+ VM_OBJECT_TRYWLOCK(obj)) {
/* Only free unmapped pages. */
if (obj->ref_count == 0 ||
!pmap_page_is_mapped(pg))
@@ -153,13 +154,24 @@
* locked cannot be relied upon.
*/
freed = vm_page_try_to_free(pg);
- else
- freed = false;
VM_OBJECT_WUNLOCK(obj);
- if (!freed)
+ }
+ if (!freed) {
+ /*
+ * If we were asked to not cache the page, place
+ * it near the head of the inactive queue so
+ * that it is reclaimed sooner. Otherwise,
+ * maintain LRU.
+ */
+ if (nocache)
vm_page_deactivate_noreuse(pg);
- } else
- vm_page_deactivate_noreuse(pg);
+ else if (pg->queue == PQ_ACTIVE)
+ vm_page_reference(pg);
+ else if (pg->queue != PQ_INACTIVE)
+ vm_page_deactivate(pg);
+ else
+ vm_page_requeue(pg);
+ }
}
}
vm_page_unlock(pg);
Index: head/sys/kern/vfs_bio.c
===================================================================
--- head/sys/kern/vfs_bio.c
+++ head/sys/kern/vfs_bio.c
@@ -2621,7 +2621,7 @@
bool freed;
vm_page_lock(m);
- if (vm_page_unwire(m, PQ_NONE)) {
+ if (vm_page_unwire_noq(m)) {
/*
* Determine if the page should be freed before adding
* it to the inactive queue.
@@ -2637,14 +2637,16 @@
if (!freed) {
/*
* If the page is unlikely to be reused, let the
- * VM know. Otherwise, maintain LRU page
- * ordering and put the page at the tail of the
- * inactive queue.
+ * VM know. Otherwise, maintain LRU.
*/
if ((bp->b_flags & B_NOREUSE) != 0)
vm_page_deactivate_noreuse(m);
- else
+ else if (m->queue == PQ_ACTIVE)
+ vm_page_reference(m);
+ else if (m->queue != PQ_INACTIVE)
vm_page_deactivate(m);
+ else
+ vm_page_requeue(m);
}
}
vm_page_unlock(m);
Index: head/sys/vm/vm_object.c
===================================================================
--- head/sys/vm/vm_object.c
+++ head/sys/vm/vm_object.c
@@ -1275,7 +1275,7 @@
if (tm->valid != VM_PAGE_BITS_ALL)
goto next_pindex;
vm_page_lock(tm);
- if (tm->hold_count != 0 || tm->wire_count != 0) {
+ if (vm_page_held(tm)) {
vm_page_unlock(tm);
goto next_pindex;
}
Index: head/sys/vm/vm_page.h
===================================================================
--- head/sys/vm/vm_page.h
+++ head/sys/vm/vm_page.h
@@ -97,7 +97,7 @@
* or the lock for either the free or paging queue (Q). If a field is
* annotated below with two of these locks, then holding either lock is
* sufficient for read access, but both locks are required for write
- * access.
+ * access. An annotation of (C) indicates that the field is immutable.
*
* In contrast, the synchronization of accesses to the page's
* dirty field is machine dependent (M). In the
@@ -111,6 +111,38 @@
* contains the dirty field. In the machine-independent layer,
* the implementation of read-modify-write operations on the
* field is encapsulated in vm_page_clear_dirty_mask().
+ *
+ * The page structure contains two counters which prevent page reuse.
+ * Both counters are protected by the page lock (P). The hold
+ * counter counts transient references obtained via a pmap lookup, and
+ * is also used to prevent page reclamation in situations where it is
+ * undesirable to block other accesses to the page. The wire counter
+ * is used to implement mlock(2) and is non-zero for pages containing
+ * kernel memory. Pages that are wired or held will not be reclaimed
+ * or laundered by the page daemon, but are treated differently during
+ * a page queue scan: held pages remain at their position in the queue,
+ * while wired pages are removed from the queue and must later be
+ * re-enqueued appropriately by the unwiring thread. It is legal to
+ * call vm_page_free() on a held page; doing so causes it to be removed
+ * from its object and page queue, and the page is released to the
+ * allocator once the last hold reference is dropped. In contrast,
+ * wired pages may not be freed.
+ *
+ * In some pmap implementations, the wire count of a page table page is
+ * used to track the number of populated entries.
+ *
+ * The busy lock is an embedded reader-writer lock which protects the
+ * page's contents and identity (i.e., its <object, pindex> tuple) and
+ * interlocks with the object lock (O). In particular, a page may be
+ * busied or unbusied only with the object write lock held. To avoid
+ * bloating the page structure, the busy lock lacks some of the
+ * features available to the kernel's general-purpose synchronization
+ * primitives. As a result, busy lock ordering rules are not verified,
+ * lock recursion is not detected, and an attempt to xbusy a busy page
+ * or sbusy an xbusy page results will trigger a panic rather than
+ * causing the thread to block. vm_page_sleep_if_busy() can be used to
+ * sleep until the page's busy state changes, after which the caller
+ * must re-lookup the page and re-evaluate its state.
*/
#if PAGE_SIZE == 4096
@@ -152,9 +184,9 @@
uint8_t oflags; /* page VPO_* flags (O) */
uint8_t queue; /* page queue index (P,Q) */
int8_t psind; /* pagesizes[] index (O) */
- int8_t segind;
+ int8_t segind; /* vm_phys segment index (C) */
uint8_t order; /* index of the buddy queue */
- uint8_t pool;
+ uint8_t pool; /* vm_phys freepool index (Q) */
u_char act_count; /* page usage count (P) */
/* NOTE that these must support one bit per DEV_BSIZE in a page */
/* so, on normal X86 kernels, they must be at least 8 bits wide */
@@ -489,7 +521,8 @@
int vm_page_trysbusy(vm_page_t m);
void vm_page_unhold_pages(vm_page_t *ma, int count);
void vm_page_unswappable(vm_page_t m);
-boolean_t vm_page_unwire(vm_page_t m, uint8_t queue);
+bool vm_page_unwire(vm_page_t m, uint8_t queue);
+bool vm_page_unwire_noq(vm_page_t m);
void vm_page_updatefake(vm_page_t m, vm_paddr_t paddr, vm_memattr_t memattr);
void vm_page_wire (vm_page_t);
void vm_page_xunbusy_hard(vm_page_t m);
@@ -714,6 +747,18 @@
{
return (m->queue == PQ_LAUNDRY || m->queue == PQ_UNSWAPPABLE);
+}
+
+/*
+ * vm_page_held:
+ *
+ * Return true if a reference prevents the page from being reclaimable.
+ */
+static inline bool
+vm_page_held(vm_page_t m)
+{
+
+ return (m->hold_count > 0 || m->wire_count > 0);
}
#endif /* _KERNEL */
Index: head/sys/vm/vm_page.c
===================================================================
--- head/sys/vm/vm_page.c
+++ head/sys/vm/vm_page.c
@@ -2053,8 +2053,7 @@
KASSERT(m->object == NULL, ("page %p has object", m));
KASSERT(m->queue == PQ_NONE,
("page %p has unexpected queue %d", m, m->queue));
- KASSERT(m->wire_count == 0, ("page %p is wired", m));
- KASSERT(m->hold_count == 0, ("page %p is held", m));
+ KASSERT(!vm_page_held(m), ("page %p is held", m));
KASSERT(!vm_page_busied(m), ("page %p is busy", m));
KASSERT(m->dirty == 0, ("page %p is dirty", m));
KASSERT(pmap_page_get_memattr(m) == VM_MEMATTR_DEFAULT,
@@ -2220,7 +2219,7 @@
vm_page_change_lock(m, &m_mtx);
m_inc = 1;
retry:
- if (m->wire_count != 0 || m->hold_count != 0)
+ if (vm_page_held(m))
run_ext = 0;
#if VM_NRESERVLEVEL > 0
else if ((level = vm_reserv_level(m)) >= 0 &&
@@ -2248,8 +2247,7 @@
*/
VM_OBJECT_RUNLOCK(object);
goto retry;
- } else if (m->wire_count != 0 ||
- m->hold_count != 0) {
+ } else if (vm_page_held(m)) {
run_ext = 0;
goto unlock;
}
@@ -2391,7 +2389,7 @@
*/
vm_page_change_lock(m, &m_mtx);
retry:
- if (m->wire_count != 0 || m->hold_count != 0)
+ if (vm_page_held(m))
error = EBUSY;
else if ((object = m->object) != NULL) {
/*
@@ -2408,8 +2406,7 @@
*/
VM_OBJECT_WUNLOCK(object);
goto retry;
- } else if (m->wire_count != 0 ||
- m->hold_count != 0) {
+ } else if (vm_page_held(m)) {
error = EBUSY;
goto unlock;
}
@@ -3042,9 +3039,7 @@
if (queue != PQ_NONE)
vm_page_dequeue(m);
vm_page_enqueue(PQ_ACTIVE, m);
- } else
- KASSERT(queue == PQ_NONE,
- ("vm_page_activate: wired page %p is queued", m));
+ }
} else {
if (m->act_count < ACT_INIT)
m->act_count = ACT_INIT;
@@ -3241,26 +3236,18 @@
}
/*
- * vm_page_wire:
+ * vm_page_wire:
*
- * Mark this page as wired down by yet
- * another map, removing it from paging queues
- * as necessary.
+ * Mark this page as wired down. If the page is fictitious, then
+ * its wire count must remain one.
*
- * If the page is fictitious, then its wire count must remain one.
- *
- * The page must be locked.
+ * The page must be locked.
*/
void
vm_page_wire(vm_page_t m)
{
- /*
- * Only bump the wire statistics if the page is not already wired,
- * and only unqueue the page if it is on some queue (if it is unmanaged
- * it is already off the queues).
- */
- vm_page_lock_assert(m, MA_OWNED);
+ vm_page_assert_locked(m);
if ((m->flags & PG_FICTITIOUS) != 0) {
KASSERT(m->wire_count == 1,
("vm_page_wire: fictitious page %p's wire count isn't one",
@@ -3271,7 +3258,6 @@
KASSERT((m->oflags & VPO_UNMANAGED) == 0 ||
m->queue == PQ_NONE,
("vm_page_wire: unmanaged page %p is queued", m));
- vm_page_remque(m);
atomic_add_int(&vm_cnt.v_wire_count, 1);
}
m->wire_count++;
@@ -3288,38 +3274,69 @@
* Only managed pages belonging to an object can be paged out. If the number
* of wirings transitions to zero and the page is eligible for page out, then
* the page is added to the specified paging queue (unless PQ_NONE is
- * specified).
+ * specified, in which case the page is dequeued if it belongs to a paging
+ * queue).
*
* If a page is fictitious, then its wire count must always be one.
*
* A managed page must be locked.
*/
-boolean_t
+bool
vm_page_unwire(vm_page_t m, uint8_t queue)
{
+ bool unwired;
KASSERT(queue < PQ_COUNT || queue == PQ_NONE,
("vm_page_unwire: invalid queue %u request for page %p",
queue, m));
+
+ unwired = vm_page_unwire_noq(m);
+ if (unwired && (m->oflags & VPO_UNMANAGED) == 0 && m->object != NULL) {
+ if (m->queue == queue) {
+ if (queue == PQ_ACTIVE)
+ vm_page_reference(m);
+ else if (queue != PQ_NONE)
+ vm_page_requeue(m);
+ } else {
+ vm_page_remque(m);
+ if (queue != PQ_NONE) {
+ vm_page_enqueue(queue, m);
+ if (queue == PQ_ACTIVE)
+ /* Initialize act_count. */
+ vm_page_activate(m);
+ }
+ }
+ }
+ return (unwired);
+}
+
+/*
+ *
+ * vm_page_unwire_noq:
+ *
+ * Unwire a page without (re-)inserting it into a page queue. It is up
+ * to the caller to enqueue, requeue, or free the page as appropriate.
+ * In most cases, vm_page_unwire() should be used instead.
+ */
+bool
+vm_page_unwire_noq(vm_page_t m)
+{
+
if ((m->oflags & VPO_UNMANAGED) == 0)
vm_page_assert_locked(m);
if ((m->flags & PG_FICTITIOUS) != 0) {
KASSERT(m->wire_count == 1,
("vm_page_unwire: fictitious page %p's wire count isn't one", m));
- return (FALSE);
+ return (false);
}
- if (m->wire_count > 0) {
- m->wire_count--;
- if (m->wire_count == 0) {
- atomic_subtract_int(&vm_cnt.v_wire_count, 1);
- if ((m->oflags & VPO_UNMANAGED) == 0 &&
- m->object != NULL && queue != PQ_NONE)
- vm_page_enqueue(queue, m);
- return (TRUE);
- } else
- return (FALSE);
- } else
+ if (m->wire_count == 0)
panic("vm_page_unwire: page %p's wire count is zero", m);
+ m->wire_count--;
+ if (m->wire_count == 0) {
+ atomic_subtract_int(&vm_cnt.v_wire_count, 1);
+ return (true);
+ } else
+ return (false);
}
/*
@@ -3448,8 +3465,7 @@
vm_page_assert_locked(m);
VM_OBJECT_ASSERT_WLOCKED(m->object);
KASSERT((m->oflags & VPO_UNMANAGED) == 0, ("page %p is unmanaged", m));
- if (m->dirty != 0 || m->hold_count != 0 || m->wire_count != 0 ||
- vm_page_busied(m))
+ if (m->dirty != 0 || vm_page_held(m) || vm_page_busied(m))
return (false);
if (m->object->ref_count != 0) {
pmap_remove_all(m);
Index: head/sys/vm/vm_pageout.c
===================================================================
--- head/sys/vm/vm_pageout.c
+++ head/sys/vm/vm_pageout.c
@@ -335,11 +335,8 @@
VM_OBJECT_ASSERT_WLOCKED(object);
pindex = m->pindex;
- /*
- * We can't clean the page if it is busy or held.
- */
vm_page_assert_unbusied(m);
- KASSERT(m->hold_count == 0, ("page %p is held", m));
+ KASSERT(!vm_page_held(m), ("page %p is held", m));
pmap_remove_write(m);
vm_page_unlock(m);
@@ -378,8 +375,7 @@
break;
}
vm_page_lock(p);
- if (!vm_page_in_laundry(p) ||
- p->hold_count != 0) { /* may be undergoing I/O */
+ if (!vm_page_in_laundry(p) || vm_page_held(p)) {
vm_page_unlock(p);
ib = 0;
break;
@@ -405,8 +401,7 @@
if (p->dirty == 0)
break;
vm_page_lock(p);
- if (!vm_page_in_laundry(p) ||
- p->hold_count != 0) { /* may be undergoing I/O */
+ if (!vm_page_in_laundry(p) || vm_page_held(p)) {
vm_page_unlock(p);
break;
}
@@ -655,10 +650,10 @@
}
/*
- * The page may have been busied or held while the object
+ * The page may have been busied or referenced while the object
* and page locks were released.
*/
- if (vm_page_busied(m) || m->hold_count != 0) {
+ if (vm_page_busied(m) || vm_page_held(m)) {
vm_page_unlock(m);
error = EBUSY;
goto unlock_all;
@@ -747,11 +742,18 @@
vm_page_unlock(m);
continue;
}
+ if (m->wire_count != 0) {
+ vm_page_dequeue_locked(m);
+ vm_page_unlock(m);
+ continue;
+ }
object = m->object;
if ((!VM_OBJECT_TRYWLOCK(object) &&
(!vm_pageout_fallback_object_lock(m, &next) ||
- m->hold_count != 0)) || vm_page_busied(m)) {
+ vm_page_held(m))) || vm_page_busied(m)) {
VM_OBJECT_WUNLOCK(object);
+ if (m->wire_count != 0 && vm_page_pagequeue(m) == pq)
+ vm_page_dequeue_locked(m);
vm_page_unlock(m);
continue;
}
@@ -1190,8 +1192,17 @@
*/
if (!vm_pageout_page_lock(m, &next))
goto unlock_page;
- else if (m->hold_count != 0) {
+ else if (m->wire_count != 0) {
/*
+ * Wired pages may not be freed, and unwiring a queued
+ * page will cause it to be requeued. Thus, remove them
+ * from the queue now to avoid unnecessary revisits.
+ */
+ vm_page_dequeue_locked(m);
+ addl_page_shortage++;
+ goto unlock_page;
+ } else if (m->hold_count != 0) {
+ /*
* Held pages are essentially stuck in the
* queue. So, they ought to be discounted
* from the inactive count. See the
@@ -1205,9 +1216,13 @@
if (!VM_OBJECT_TRYWLOCK(object)) {
if (!vm_pageout_fallback_object_lock(m, &next))
goto unlock_object;
- else if (m->hold_count != 0) {
+ else if (m->wire_count != 0) {
+ vm_page_dequeue_locked(m);
addl_page_shortage++;
goto unlock_object;
+ } else if (m->hold_count != 0) {
+ addl_page_shortage++;
+ goto unlock_object;
}
}
if (vm_page_busied(m)) {
@@ -1226,7 +1241,7 @@
vm_page_unlock(m);
continue;
}
- KASSERT(m->hold_count == 0, ("Held page %p", m));
+ KASSERT(!vm_page_held(m), ("Held page %p", m));
/*
* Dequeue the inactive page and unlock the inactive page
@@ -1431,6 +1446,15 @@
* the page for eligibility.
*/
VM_CNT_INC(v_pdpages);
+
+ /*
+ * Wired pages are dequeued lazily.
+ */
+ if (m->wire_count != 0) {
+ vm_page_dequeue_locked(m);
+ vm_page_unlock(m);
+ continue;
+ }
/*
* Check to see "how much" the page has been used.
Index: head/sys/vm/vm_swapout.c
===================================================================
--- head/sys/vm/vm_swapout.c
+++ head/sys/vm/vm_swapout.c
@@ -209,7 +209,7 @@
continue;
VM_CNT_INC(v_pdpages);
vm_page_lock(p);
- if (p->wire_count != 0 || p->hold_count != 0 ||
+ if (vm_page_held(p) ||
!pmap_page_exists_quick(pmap, p)) {
vm_page_unlock(p);
continue;

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