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- Eliminate the vm object lock from the active queue scan. It is not

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necessary since we do not free or cache the page from active anymore.
   Document the one possible race that is harmless.

Sponsored by:	EMC / Isilon Storage Division
Discussed with:	alc
This commit is contained in:
Jeff Roberson 2013-08-21 22:39:19 +00:00
parent 7261b203c6
commit 274132ac23
1 changed files with 9 additions and 24 deletions
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33
sys/vm/vm_pageout.c
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@ -1333,25 +1333,6 @@ relock_queues:
m = next;
continue;
}
object = m->object;
if (!VM_OBJECT_TRYWLOCK(object) &&
!vm_pageout_fallback_object_lock(m, &next)) {
VM_OBJECT_WUNLOCK(object);
vm_page_unlock(m);
m = next;
continue;
}
/*
* Don't deactivate pages that are busy.
*/
if (vm_page_busied(m) || m->hold_count != 0) {
vm_page_unlock(m);
VM_OBJECT_WUNLOCK(object);
vm_page_requeue_locked(m);
m = next;
continue;
}
/*
* The count for pagedaemon pages is done after checking the
@ -1367,7 +1348,15 @@ relock_queues:
vm_page_aflag_clear(m, PGA_REFERENCED);
act_delta += 1;
}
if (object->ref_count != 0)
/*
* Unlocked object ref count check. Two races are possible.
* 1) The ref was transitioning to zero and we saw non-zero,
* the pmap bits will be checked unnecessarily.
* 2) The ref was transitioning to one and we saw zero.
* The page lock prevents a new reference to this page so
* we need not check the reference bits.
*/
if (m->object->ref_count != 0)
act_delta += pmap_ts_referenced(m);
/*
@ -1387,9 +1376,6 @@ relock_queues:
* queue depending on usage.
*/
if (act_delta == 0) {
KASSERT(object->ref_count != 0 ||
!pmap_page_is_mapped(m),
("vm_pageout_scan: page %p is mapped", m));
/* Dequeue to avoid later lock recursion. */
vm_page_dequeue_locked(m);
vm_page_deactivate(m);
@ -1397,7 +1383,6 @@ relock_queues:
} else
vm_page_requeue_locked(m);
vm_page_unlock(m);
VM_OBJECT_WUNLOCK(object);
m = next;
}
vm_pagequeue_unlock(pq);