It makes no sense for vm_page_sleep_if_busy()'s helper, vm_page_sleep(),

to unconditionally set PG_REFERENCED on a page before sleeping.  In many
cases, it's perfectly ok for the page to disappear, i.e., be reclaimed by
the page daemon, before the caller to vm_page_sleep() is reawakened.
Instead, we now explicitly set PG_REFERENCED in those cases where having
the page persist until the caller is awakened is clearly desirable.  Note,
however, that setting PG_REFERENCED on the page is still only a hint,
and not a guarantee that the page should persist.

1 files changed, 6 insertions, 0 deletions

diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index d9cf63e..5ee4ab4 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -338,6 +338,12 @@ RetryFault:;
 			 * to pmap it.
 			 */
 			if ((fs.m->oflags & VPO_BUSY) || fs.m->busy) {
+				/*
+				 * Reference the page before unlocking and
+				 * sleeping so that the page daemon is less
+				 * likely to reclaim it. 
+				 */
+				vm_page_flag_set(fs.m, PG_REFERENCED);
 				vm_page_unlock_queues();
 				vm_page_unlock(fs.m);
 				VM_OBJECT_UNLOCK(fs.object);