linux-kernel - Re: [PATCH 3/4] mm, compaction: ignore fragindex from compaction_zonelist

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Date:   Thu, 29 Sep 2016 11:57:01 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Arkadiusz Miskiewicz <a.miskiewicz@...il.com>,
        Ralf-Peter Rohbeck <Ralf-Peter.Rohbeck@...ntum.com>,
        Olaf Hering <olaf@...fle.de>, Michal Hocko <mhocko@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Rientjes <rientjes@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 3/4] mm, compaction: ignore fragindex from
 compaction_zonelist_suitable()

On 09/26/2016 06:20 PM, Vlastimil Babka wrote:
> The compaction_zonelist_suitable() function tries to determine if compaction
> will be able to proceed after sufficient reclaim, i.e. whether there are
> enough reclaimable pages to provide enough order-0 freepages for compaction.
> 
> This addition of reclaimable pages to the free pages works well for the order-0
> watermark check, but in the fragmentation index check we only consider truly
> free pages. Thus we can get fragindex value close to 0 which indicates failure
> do to lack of memory, and wrongly decide that compaction won't be suitable even
> after reclaim.
> 
> Instead of trying to somehow adjust fragindex for reclaimable pages, let's just
> skip it from compaction_zonelist_suitable().
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Rik van Riel <riel@...hat.com>

Bah, a fix below, sorry.
----8<----
>From 1cd4855305a9c7eef0cf0c1af9f310cecdcc9406 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@...e.cz>
Date: Thu, 29 Sep 2016 11:54:07 +0200
Subject: [PATCH] mm, compaction: ignore fragindex from
 compaction_zonelist_suitable()-fix

COMPACT_NOT_SUITABLE_ZONE should not leak outside compaction_suitable() and
we should not skip tracepoint.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/compaction.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index badb92bf14b4..0409a4ad6ea1 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1445,7 +1445,7 @@ enum compact_result compaction_suitable(struct zone *zone, int order,
 	if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
 		fragindex = fragmentation_index(zone, order);
 		if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
-			return COMPACT_NOT_SUITABLE_ZONE;
+			ret = COMPACT_NOT_SUITABLE_ZONE;
 	}
 
 	trace_mm_compaction_suitable(zone, order, ret);
-- 
2.10.0