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Index: sys/vm/vm_page.h
===================================================================
--- sys/vm/vm_page.h
+++ sys/vm/vm_page.h
@@ -109,6 +109,22 @@
* 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().
+ *
+ * Two types of page structure references exist: holds and wires.
+ * Holds are short-term references which prevent the page from being freed
+ * and reused for another purpose. However, it is legal to call
+ * vm_page_free() on a held page, in which case the page will be removed
+ * from its paging queue (if any) and its object (if any). Wires are
+ * stronger references which indicate that the page's contents are in use.
+ * It is not legal to call vm_page_free() on a wired page. When releasing
+ * the last wiring of a page, that page may optionally be inserted at the
+ * tail of a paging queue. If the page already belongs to that queue, it
+ * is requeued to preserve LRU. Both holds and wires prevent pages from
+ * being examined by the page daemon.
+ *
+ * The wire count field of the page structure has a different meaning for
+ * page table pages on some architectures: it records the number of valid
+ * entries in the page.
*/
#if PAGE_SIZE == 4096
Index: sys/vm/vm_page.c
===================================================================
--- sys/vm/vm_page.c
+++ sys/vm/vm_page.c
@@ -2705,9 +2705,7 @@
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;
@@ -2825,9 +2823,7 @@
/*
* 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 by yet another map.
*
* If the page is fictitious, then its wire count must remain one.
*
@@ -2837,11 +2833,6 @@
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);
if ((m->flags & PG_FICTITIOUS) != 0) {
KASSERT(m->wire_count == 1,
@@ -2853,11 +2844,11 @@
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++;
- KASSERT(m->wire_count != 0, ("vm_page_wire: wire_count overflow m=%p", m));
+ if (m->wire_count == 0)
+ panic("vm_page_wire: wire_count overflow m=%p", m);
}
/*
@@ -2890,18 +2881,24 @@
("vm_page_unwire: fictitious page %p's wire count isn't one", m));
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)
+ 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);
+ if ((m->oflags & VPO_UNMANAGED) == 0 && m->object != NULL &&
+ queue != PQ_NONE) {
+ if (m->queue == queue)
+ vm_page_requeue(m);
+ else {
+ vm_page_remque(m);
vm_page_enqueue(queue, m);
- return (TRUE);
- } else
- return (FALSE);
+ }
+ }
+ return (TRUE);
} else
- panic("vm_page_unwire: page %p's wire count is zero", m);
+ return (FALSE);
}
/*
Index: sys/vm/vm_pageout.c
===================================================================
--- sys/vm/vm_pageout.c
+++ sys/vm/vm_pageout.c
@@ -397,11 +397,9 @@
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(m->wire_count == 0, ("page %p is wired", m));
vm_page_unlock(m);
mc[vm_pageout_page_count] = pb = ps = m;
@@ -439,7 +437,7 @@
}
vm_page_lock(p);
if (!vm_page_in_laundry(p) ||
- p->hold_count != 0) { /* may be undergoing I/O */
+ p->hold_count != 0 || p->wire_count != 0) {
vm_page_unlock(p);
ib = 0;
break;
@@ -465,7 +463,7 @@
break;
vm_page_lock(p);
if (!vm_page_in_laundry(p) ||
- p->hold_count != 0) { /* may be undergoing I/O */
+ p->hold_count != 0 || p->wire_count != 0) {
vm_page_unlock(p);
break;
}
@@ -870,7 +868,8 @@
* The page may have been busied or held while the object
* and page locks were released.
*/
- if (vm_page_busied(m) || m->hold_count != 0) {
+ if (vm_page_busied(m) || m->hold_count != 0 ||
+ m->wire_count != 0) {
vm_page_unlock(m);
error = EBUSY;
goto unlock_all;
@@ -959,10 +958,27 @@
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)) {
+ if (!VM_OBJECT_TRYWLOCK(object)) {
+ if (!vm_pageout_fallback_object_lock(m, &next) ||
+ m->hold_count != 0) {
+ VM_OBJECT_WUNLOCK(object);
+ vm_page_unlock(m);
+ continue;
+ }
+ if (m->wire_count != 0) {
+ VM_OBJECT_WUNLOCK(object);
+ vm_page_dequeue_locked(m);
+ vm_page_unlock(m);
+ continue;
+ }
+ }
+ if (vm_page_busied(m)) {
VM_OBJECT_WUNLOCK(object);
vm_page_unlock(m);
continue;
@@ -1399,7 +1415,16 @@
*/
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
@@ -1414,7 +1439,11 @@
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;
}
@@ -1436,6 +1465,7 @@
continue;
}
KASSERT(m->hold_count == 0, ("Held page %p", m));
+ KASSERT(m->wire_count == 0, ("Wired page %p", m));
/*
* Dequeue the inactive page and unlock the inactive page
@@ -1637,6 +1667,15 @@
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.
*/
if ((m->aflags & PGA_REFERENCED) != 0) {

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