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D14778.id40518.diff
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Index: sys/kern/vfs_bio.c
===================================================================
--- sys/kern/vfs_bio.c
+++ sys/kern/vfs_bio.c
@@ -2911,28 +2911,20 @@
static void
vfs_vmio_unwire(struct buf *bp, vm_page_t m)
{
- bool freed;
vm_page_lock(m);
if (vm_page_unwire_noq(m)) {
- /*
- * Determine if the page should be freed before adding
- * it to the inactive queue.
- */
- if (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) {
+ if ((bp->b_flags & B_DIRECT) == 0 || !vm_page_try_to_free(m)) {
/*
- * If the page is unlikely to be reused, let the
- * VM know. Otherwise, maintain LRU.
+ * Use a racy check of the valid bits to determine
+ * whether we can accelerate reclamation of the page.
+ * This allows elision of the object write lock in the
+ * common case, as buffer pages are usually valid.
+ * The B_NOREUSE flag marks data that is unlikely to be
+ * reused, so accelerate reclamation in that case too.
+ * Otherwise, maintain LRU.
*/
- if ((bp->b_flags & B_NOREUSE) != 0)
+ if (m->valid == 0 || (bp->b_flags & B_NOREUSE) != 0)
vm_page_deactivate_noreuse(m);
else if (m->queue == PQ_ACTIVE)
vm_page_reference(m);
@@ -3019,7 +3011,12 @@
(desiredpages << PAGE_SHIFT), bp->b_npages - desiredpages);
} else
BUF_CHECK_UNMAPPED(bp);
- obj = bp->b_bufobj->bo_object;
+
+ /*
+ * The object lock is needed only if we attempt to free the buffer's
+ * pages.
+ */
+ obj = (bp->b_flags & B_DIRECT) != 0 ? bp->b_bufobj->bo_object : NULL;
if (obj != NULL)
VM_OBJECT_WLOCK(obj);
for (i = desiredpages; i < bp->b_npages; i++) {

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