Author: alc
Date: Tue Sep 22 18:16:52 2015
New Revision: 288122
URL: https://svnweb.freebsd.org/changeset/base/288122
Log:
Change vm_page_unwire() such that it (1) accepts PQ_NONE as the specified
queue and (2) returns a Boolean indicating whether the page's wire count
transitioned to zero.
Exploit this change in vfs_vmio_release() to avoid pointlessly enqueueing
a page that is about to be freed.
(An earlier version of this change was developed by attilio@ and kmacy@.
Any errors in this version are my own.)
Reviewed by: kib
Sponsored by: EMC / Isilon Storage Division
Modified:
head/sys/kern/vfs_bio.c
head/sys/vm/vm_page.c
head/sys/vm/vm_page.h
Modified: head/sys/kern/vfs_bio.c
==============================================================================
--- head/sys/kern/vfs_bio.c Tue Sep 22 17:34:51 2015 (r288121)
+++ head/sys/kern/vfs_bio.c Tue Sep 22 18:16:52 2015 (r288122)
@@ -2076,6 +2076,7 @@ vfs_vmio_release(struct buf *bp)
vm_object_t obj;
vm_page_t m;
int i;
+ bool freed;
if (buf_mapped(bp)) {
BUF_CHECK_MAPPED(bp);
@@ -2088,23 +2089,28 @@ vfs_vmio_release(struct buf *bp)
for (i = 0; i < bp->b_npages; i++) {
m = bp->b_pages[i];
bp->b_pages[i] = NULL;
- /*
- * In order to keep page LRU ordering consistent, put
- * everything on the inactive queue.
- */
vm_page_lock(m);
- vm_page_unwire(m, PQ_INACTIVE);
-
- /*
- * Might as well free the page if we can and it has
- * no valid data. We also free the page if the
- * buffer was used for direct I/O
- */
- if ((bp->b_flags & B_ASYNC) == 0 && !m->valid) {
- if (m->wire_count == 0 && !vm_page_busied(m))
- vm_page_free(m);
- } else if (bp->b_flags & B_DIRECT)
- vm_page_try_to_free(m);
+ if (vm_page_unwire(m, PQ_NONE)) {
+ /*
+ * Determine if the page should be freed before adding
+ * it to the inactive queue.
+ */
+ if ((bp->b_flags & B_ASYNC) == 0 && m->valid == 0) {
+ freed = !vm_page_busied(m);
+ if (freed)
+ vm_page_free(m);
+ } else if ((bp->b_flags & B_DIRECT) != 0)
+ freed = vm_page_try_to_free(m);
+ else
+ freed = false;
+ if (!freed) {
+ /*
+ * In order to maintain LRU page ordering, put
+ * the page at the tail of the inactive queue.
+ */
+ vm_page_deactivate(m);
+ }
+ }
vm_page_unlock(m);
}
if (obj != NULL)
Modified: head/sys/vm/vm_page.c
==============================================================================
--- head/sys/vm/vm_page.c Tue Sep 22 17:34:51 2015 (r288121)
+++ head/sys/vm/vm_page.c Tue Sep 22 18:16:52 2015 (r288122)
@@ -2476,42 +2476,46 @@ vm_page_wire(vm_page_t m)
/*
* vm_page_unwire:
*
- * Release one wiring of the specified page, potentially enabling it to be
- * paged again. If paging is enabled, then the value of the parameter
- * "queue" determines the queue to which the page is added.
- *
- * However, unless the page belongs to an object, it is not enqueued because
- * it cannot be paged out.
+ * Release one wiring of the specified page, potentially allowing it to be
+ * paged out. Returns TRUE if the number of wirings transitions to zero and
+ * FALSE otherwise.
+ *
+ * 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).
*
* If a page is fictitious, then its wire count must always be one.
*
* A managed page must be locked.
*/
-void
+boolean_t
vm_page_unwire(vm_page_t m, uint8_t queue)
{
- KASSERT(queue < PQ_COUNT,
+ KASSERT(queue < PQ_COUNT || queue == PQ_NONE,
("vm_page_unwire: invalid queue %u request for page %p",
queue, m));
if ((m->oflags & VPO_UNMANAGED) == 0)
- 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_unwire: fictitious page %p's wire count isn't one", m));
- return;
+ 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)
- return;
- if (queue == PQ_INACTIVE)
- m->flags &= ~PG_WINATCFLS;
- vm_page_enqueue(queue, m);
- }
+ if ((m->oflags & VPO_UNMANAGED) == 0 &&
+ m->object != NULL && queue != PQ_NONE) {
+ if (queue == PQ_INACTIVE)
+ m->flags &= ~PG_WINATCFLS;
+ vm_page_enqueue(queue, m);
+ }
+ return (TRUE);
+ } else
+ return (FALSE);
} else
panic("vm_page_unwire: page %p's wire count is zero", m);
}
Modified: head/sys/vm/vm_page.h
==============================================================================
--- head/sys/vm/vm_page.h Tue Sep 22 17:34:51 2015 (r288121)
+++ head/sys/vm/vm_page.h Tue Sep 22 18:16:52 2015 (r288122)
@@ -480,7 +480,7 @@ vm_offset_t vm_page_startup(vm_offset_t
void vm_page_sunbusy(vm_page_t m);
int vm_page_trysbusy(vm_page_t m);
void vm_page_unhold_pages(vm_page_t *ma, int count);
-void vm_page_unwire (vm_page_t m, uint8_t queue);
+boolean_t vm_page_unwire(vm_page_t m, uint8_t queue);
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);
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