[PATCH] ignore referenced pages on reclaim when OOM

[PATCH] ignore referenced pages on reclaim when OOM

[Marcelo Tosatti]

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 <riel@redhat.com> -----

From: Rik van Riel <riel@redhat.com>
Date: Fri, 5 Nov 2004 16:56:17 -0500 (EST)
To: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Subject: [PATCH] fix OOM problem
X-X-Sender: riel@chimarrao.boston.redhat.com
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 =====
--- 1.231/mm/vmscan.c	Sun Oct 17 01:07:24 2004
+++ edited/mm/vmscan.c	Mon Oct 25 17:38:56 2004
@@ -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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Re: [PATCH] ignore referenced pages on reclaim when OOM

[Marcelo Tosatti]

On Mon, Nov 08, 2004 at 04:56:25PM -0500, Rik van Riel wrote:
> On Tue, 9 Nov 2004, Nikita Danilov wrote:
> 
> >  > 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).
> 
> 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.

Nikita, 

Can you please rerun your tests with priority=0 instead of priority=2? 
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Re: [PATCH] ignore referenced pages on reclaim when OOM

[Nikita Danilov]

Marcelo Tosatti writes:
 > 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.

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).

Nikita.

 > 
 > ----- Forwarded message from Rik van Riel <riel@redhat.com> -----
 > 
 > From: Rik van Riel <riel@redhat.com>
 > Date: Fri, 5 Nov 2004 16:56:17 -0500 (EST)
 > To: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
 > Subject: [PATCH] fix OOM problem
 > X-X-Sender: riel@chimarrao.boston.redhat.com
 > 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 =====
 > --- 1.231/mm/vmscan.c	Sun Oct 17 01:07:24 2004
 > +++ edited/mm/vmscan.c	Mon Oct 25 17:38:56 2004
 > @@ -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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Re: [PATCH] ignore referenced pages on reclaim when OOM

[Rik van Riel]

On Tue, 9 Nov 2004, Nikita Danilov wrote:

>  > 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).

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.

-- 
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan

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Re: [PATCH] ignore referenced pages on reclaim when OOM

[Andrew Morton]

Rik van Riel <riel@redhat.com> wrote:
>
> On Tue, 9 Nov 2004, Nikita Danilov wrote:
> 
> >  > 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).
> 
> 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.
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Re: [PATCH] ignore referenced pages on reclaim when OOM

[Marcelo Tosatti]

On Mon, Nov 08, 2004 at 02:28:37PM -0800, Andrew Morton wrote:
> Rik van Riel <riel@redhat.com> wrote:
> >
> > On Tue, 9 Nov 2004, Nikita Danilov wrote:
> > 
> > >  > 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).
> > 
> > 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.

You know, all_unreclaimable has drawbacks.

Its hard to know whether you have "scanned enough to consider the box OOM 
and trigger OOM killer" when all_unreclaimable avoids the system 
from "scanning enough".

I'm trying to improve the OOM-kill-from-kswapd patch but z->all_unreclaimable 
is currently the bigger "rock on the shoe" - we need some way to detect that
the zones have been scanned enough so to be able to say 
"OK, I have scanned enough and no freeable pages appear, its time 
to trigger the OOM killer".

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

There must be some way to combine both effectively.

This is my current patch - avoids spurious OOM kills but obviously 
fails to set "worked_dma" - "worked_normal" due to all_unreclaimable logic,  
resulting in livelock when swapspace exhauts. 

Ideas are welcome.


--- vmscan.c.orig	2004-11-09 16:38:04.000000000 -0200
+++ vmscan.c	2004-11-10 18:59:43.098090736 -0200
@@ -878,6 +878,8 @@
 		shrink_zone(zone, sc);
 	}
 }
+
+int task_looping_oom = 0;
  
 /*
  * This is the main entry point to direct page reclaim.
@@ -952,8 +954,8 @@
 		if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
 			blk_congestion_wait(WRITE, HZ/10);
 	}
-	if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY))
-		out_of_memory(gfp_mask);
+        if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY))
+		task_looping_oom = 1;
 out:
 	for (i = 0; zones[i] != 0; i++) {
 		struct zone *zone = zones[i];
@@ -963,6 +965,8 @@
 
 		zone->prev_priority = zone->temp_priority;
 	}
+	if (ret)
+		task_looping_oom = 0;
 	return ret;
 }
 
@@ -997,13 +1001,17 @@
 	int all_zones_ok;
 	int priority;
 	int i;
-	int total_scanned, total_reclaimed;
+	int total_scanned, total_reclaimed, low_reclaimed;
+	int worked_norm, worked_dma;
 	struct reclaim_state *reclaim_state = current->reclaim_state;
 	struct scan_control sc;
 
+
 loop_again:
 	total_scanned = 0;
 	total_reclaimed = 0;
+	low_reclaimed = 0;
+	worked_norm = worked_dma = 0;
 	sc.gfp_mask = GFP_KERNEL;
 	sc.may_writepage = 0;
 	sc.nr_mapped = read_page_state(nr_mapped);
@@ -1072,6 +1080,17 @@
 			if (zone->all_unreclaimable && priority != DEF_PRIORITY)
 				continue;
 
+			/* if we're scanning dma or normal, and priority 
+			 * reached zero, set "worked_dma" or "worked_norm" 
+			 * accordingly.
+			 */
+			if (i <= 1 && priority == 0) {
+				if (!i) 
+					worked_dma = 1;
+				else
+					worked_norm = 1;
+			}
+
 			if (nr_pages == 0) {	/* Not software suspend */
 				if (!zone_watermark_ok(zone, order,
 						zone->pages_high, end_zone, 0, 0))
@@ -1088,6 +1107,10 @@
 			shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages);
 			sc.nr_reclaimed += reclaim_state->reclaimed_slab;
 			total_reclaimed += sc.nr_reclaimed;
+
+			if (i <= 1)
+				low_reclaimed += sc.nr_reclaimed;
+
 			if (zone->all_unreclaimable)
 				continue;
 			if (zone->pages_scanned >= (zone->nr_active +
@@ -1128,6 +1151,29 @@
 
 		zone->prev_priority = zone->temp_priority;
 	}
+
+
+	if (!low_reclaimed && worked_dma && worked_norm && task_looping_oom) {
+
+		printk(KERN_ERR "kswp: pri:%d tot_recl:%d wrkd_dma:%d"
+				"wrkd_norm:%d tsk_loop_oom:%d\n",
+			priority, total_reclaimed, worked_dma, worked_norm, 
+				task_looping_oom);
+
+		/* 
+		 * Only kill if ZONE_NORMAL/ZONE_DMA are both below
+		 * pages_min
+		 */
+		for (i = pgdat->nr_zones - 2; i >= 0; i--) {
+			struct zone *zone = pgdat->node_zones + i;
+
+			if (zone->free_pages > zone->pages_min)
+				return 0;
+		}
+		out_of_memory(GFP_KERNEL);
+		task_looping_oom = 0;
+	}
+
 	if (!all_zones_ok) {
 		cond_resched();
 		goto loop_again;
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Re: [PATCH] ignore referenced pages on reclaim when OOM

[Marcelo Tosatti]

On Wed, Nov 10, 2004 at 02:29:00PM -0800, Andrew Morton wrote:
> Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
> >
> > 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.

The thing is - if you dont scan the zones "enough" you have no way of 
reliably knowing it is OOM.

But on the other hand, scanning it wastes CPU time - what you call "mad scanning".

They are two extremes, I feel we need a balance between them.

> 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. 

I dont think all_unreclaimable logic is rotted - it does what what it is
expected to do. 

At least thats how I see things, maybe I'm wrong and it is indeed rotted.

> Have you tried simply disabling it?

Tried now - if I disable it then balance_pgdat() detects the OOM situation by noticing
its not successful freeing pages (thus setting worked_dma and worked_normal, 
see patch), and kills the memory hog. Side note, the memory hog runs _much_ faster
without all_unreclaimable logic.

I'll continue hacking on this tomorrow.

As always, thanks for the input :D

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Re: [PATCH] ignore referenced pages on reclaim when OOM

[Andrew Morton]

Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
>
> 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?
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Re: [PATCH] ignore referenced pages on reclaim when OOM

[Rik van Riel]

On Wed, 10 Nov 2004, Andrew Morton wrote:

> 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.

The swap token logic can make it appear like this is the case,
unless you ignore the referenced bit when you reach priority 0.

-- 
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan
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