svn commit: r206768 - head/sys/vm
Alan Cox
alc at FreeBSD.org
Sat Apr 17 18:35:07 UTC 2010
Author: alc
Date: Sat Apr 17 18:35:07 2010
New Revision: 206768
URL: http://svn.freebsd.org/changeset/base/206768
Log:
In vm_object_backing_scan(), setting PG_REFERENCED on a page before
sleeping on that page is nonsensical. Doing so reduces the likelihood
that the page daemon will reclaim the page before the thread waiting in
vm_object_backing_scan() is reawakened. However, it does not guarantee
that the page is not reclaimed, so vm_object_backing_scan() restarts
after reawakening. More importantly, this muddles the meaning of
PG_REFERENCED. There is no reason to believe that the caller of
vm_object_backing_scan() is going to use (i.e., access) the contents of
the page. There is especially no reason to believe that an access is
more likely because vm_object_backing_scan() had to sleep on the page.
Discussed with: kib
MFC after: 3 weeks
Modified:
head/sys/vm/vm_object.c
Modified: head/sys/vm/vm_object.c
==============================================================================
--- head/sys/vm/vm_object.c Sat Apr 17 18:18:46 2010 (r206767)
+++ head/sys/vm/vm_object.c Sat Apr 17 18:35:07 2010 (r206768)
@@ -1553,9 +1553,6 @@ vm_object_backing_scan(vm_object_t objec
}
} else if (op & OBSC_COLLAPSE_WAIT) {
if ((p->oflags & VPO_BUSY) || p->busy) {
- vm_page_lock_queues();
- vm_page_flag_set(p, PG_REFERENCED);
- vm_page_unlock_queues();
VM_OBJECT_UNLOCK(object);
p->oflags |= VPO_WANTED;
msleep(p, VM_OBJECT_MTX(backing_object),
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