ignore referenced pages on reclaim when OOM

Andrew,

Can you please apply Rik's patch?

Ignore referenced bit when priority reaches 0. Get out of such OOM situation as fast as possible, instead of running around trying to find elegible pages for reclaim.

Speeds up extreme load performance on Rik's tests.

----- Forwarded message from Rik van Riel <[email protected]> -----

From: Rik van Riel <[email protected]>
Date: Fri, 5 Nov 2004 16:56:17 -0500 (EST)
To: Marcelo Tosatti <[email protected]>
Subject: [PATCH] fix OOM problem
X-X-Sender: [email protected]
X-MIMETrack: Itemize by SMTP Server on USMail/Cyclades(Release 6.5.1|January 21, 2004) at
11/05/2004 13:58:40

===== mm/vmscan.c 1.231 vs edited =====

mm/vmscan.c +2 -3

@@ -379,7 +379,7 @@
 
 		referenced = page_referenced(page, 1);
 		/* In active use or really unfreeable?  Activate it. */
-		if (referenced && page_mapping_inuse(page))
+		if (referenced && sc->priority && page_mapping_inuse(page))
 			goto activate_locked;
 
 #ifdef CONFIG_SWAP

@@ -715,7 +715,7 @@
 		if (page_mapped(page)) {
 			if (!reclaim_mapped ||
 			    (total_swap_pages == 0 && PageAnon(page)) ||
-			    page_referenced(page, 0)) {
+			    (page_referenced(page, 0) && sc->priority)) {
 				list_add(&page->lru, &l_active);
 				continue;
 			}
 
 
 
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Quoted 1 line

Speeds up extreme load performance on Rik's tests.

I recently tested quite similar thing, the only dfference being that in my case references bit started being ignored when scanning priority reached 2 rather than 0.

I found that it _degrades_ performance in the loads when there is a lot of file system write-back going from tail of the inactive list (like dirtying huge file through mmap in a loop).

Quoted 6 lines · Nikita Danilov

Quoted 1 line

Speeds up extreme load performance on Rik's tests.

I recently tested quite similar thing, the only dfference being that in my case references bit started being ignored when scanning priority reached 2 rather than 0.

Quoted 3 lines

I found that it _degrades_ performance in the loads when there is a lot of file system write-back going from tail of the inactive list (like dirtying huge file through mmap in a loop).

Well yeah, when you reach priority 2, you've only scanned 1/4 of memory. On the other hand, when you reach priority 0, you've already scanned all pages once - beyond that point the referenced bit really doesn't buy you much any more.

Quoted 6 lines · Nikita Danilov

Quoted 1 line

Speeds up extreme load performance on Rik's tests.

I recently tested quite similar thing, the only dfference being that in my case references bit started being ignored when scanning priority reached 2 rather than 0.

Quoted 3 lines

I found that it _degrades_ performance in the loads when there is a lot of file system write-back going from tail of the inactive list (like dirtying huge file through mmap in a loop).

Well yeah, when you reach priority 2, you've only scanned 1/4 of memory. On the other hand, when you reach priority 0, you've already scanned all pages once - beyond that point the referenced bit really doesn't buy you much any more.

Quoted 9 lines · Rik van Riel

Quoted 6 lines · Nikita Danilov

Quoted 1 line

Speeds up extreme load performance on Rik's tests.

I recently tested quite similar thing, the only dfference being that in my case references bit started being ignored when scanning priority reached 2 rather than 0.

Quoted 9 lines

Quoted 3 lines

I found that it _degrades_ performance in the loads when there is a lot of file system write-back going from tail of the inactive list (like dirtying huge file through mmap in a loop).

Well yeah, when you reach priority 2, you've only scanned 1/4 of memory. On the other hand, when you reach priority 0, you've already scanned all pages once - beyond that point the referenced bit really doesn't buy you much any more.

But we have to scan active, referenced pages two times to move them onto the inactive list. A bit more, really, because nowadays refill_inactive_zone() doesn't even run page_referenced() until it starts to reach higher scanning priorities.

So it could be that we're just not scanning enough.

So z->all_unreclaimable logic and "OOM detection" are conflicting goals.

Quoted 2 lines · Marcelo Tosatti

So z->all_unreclaimable logic and "OOM detection" are conflicting goals.

Only in a single case: where a zone is all_unreclaimable and some pages have recently become reclaimable but we don't know about it yet.

Certainly it can happen, but it sounds really unlikely to me. So I suspect that if you were to fix that problem by some means, it wouldn't help anything.

But maybe I'm wrong, or maybe the all_unreclaimable logic has rotted.

Have you tried simply disabling it?

Only in a single case: where a zone is all_unreclaimable and some pages have recently become reclaimable but we don't know about it yet.

Certainly it can happen, but it sounds really unlikely to me.