linux-kernel - Re: OOM detection regressions since 4.7

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Date:   Tue, 23 Aug 2016 09:43:40 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Markus Trippelsdorf <markus@...ppelsdorf.de>,
        Arkadiusz Miskiewicz <a.miskiewicz@...il.com>,
        Ralf-Peter Rohbeck <Ralf-Peter.Rohbeck@...ntum.com>,
        Jiri Slaby <jslaby@...e.com>, Olaf Hering <olaf@...fle.de>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Joonsoo Kim <js1304@...il.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: OOM detection regressions since 4.7

On Mon 22-08-16 15:05:17, Andrew Morton wrote:
> On Mon, 22 Aug 2016 15:42:28 +0200 Michal Hocko <mhocko@...nel.org> wrote:
> 
> > Of course, if Linus/Andrew doesn't like to take those compaction
> > improvements this late then I will ask to merge the partial revert to
> > Linus tree as well and then there is not much to discuss.
> 
> This sounds like the prudent option.  Can we get 4.8 working
> well-enough, backport that into 4.7.x and worry about the fancier stuff
> for 4.9?

OK, fair enough.

I would really appreciate if the original reporters could retest with
this patch on top of the current Linus tree. The stable backport posted
earlier doesn't apply on the current master cleanly but the change is
essentially same. mmotm tree then can revert this patch before Vlastimil
series is applied because that code is touching the currently removed
code.
---
>From 90b6b282bede7966fb6c830a6d012d2239ac40e4 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.com>
Date: Mon, 22 Aug 2016 10:52:06 +0200
Subject: [PATCH] mm, oom: prevent pre-mature OOM killer invocation for high
 order request

There have been several reports about pre-mature OOM killer invocation
in 4.7 kernel when order-2 allocation request (for the kernel stack)
invoked OOM killer even during basic workloads (light IO or even kernel
compile on some filesystems). In all reported cases the memory is
fragmented and there are no order-2+ pages available. There is usually
a large amount of slab memory (usually dentries/inodes) and further
debugging has shown that there are way too many unmovable blocks which
are skipped during the compaction. Multiple reporters have confirmed that
the current linux-next which includes [1] and [2] helped and OOMs are
not reproducible anymore.

A simpler fix for the late rc and stable is to simply ignore the
compaction feedback and retry as long as there is a reclaim progress
and we are not getting OOM for order-0 pages. We already do that for
CONFING_COMPACTION=n so let's reuse the same code when compaction is
enabled as well.

[1] http://lkml.kernel.org/r/20160810091226.6709-1-vbabka@suse.cz
[2] http://lkml.kernel.org/r/f7a9ea9d-bb88-bfd6-e340-3a933559305a@suse.cz

Fixes: 0a0337e0d1d1 ("mm, oom: rework oom detection")
Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 mm/page_alloc.c | 51 ++-------------------------------------------------
 1 file changed, 2 insertions(+), 49 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3fbe73a6fe4b..7791a03f8deb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3137,54 +3137,6 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 	return NULL;
 }
 
-static inline bool
-should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
-		     enum compact_result compact_result,
-		     enum compact_priority *compact_priority,
-		     int compaction_retries)
-{
-	int max_retries = MAX_COMPACT_RETRIES;
-
-	if (!order)
-		return false;
-
-	/*
-	 * compaction considers all the zone as desperately out of memory
-	 * so it doesn't really make much sense to retry except when the
-	 * failure could be caused by insufficient priority
-	 */
-	if (compaction_failed(compact_result)) {
-		if (*compact_priority > MIN_COMPACT_PRIORITY) {
-			(*compact_priority)--;
-			return true;
-		}
-		return false;
-	}
-
-	/*
-	 * make sure the compaction wasn't deferred or didn't bail out early
-	 * due to locks contention before we declare that we should give up.
-	 * But do not retry if the given zonelist is not suitable for
-	 * compaction.
-	 */
-	if (compaction_withdrawn(compact_result))
-		return compaction_zonelist_suitable(ac, order, alloc_flags);
-
-	/*
-	 * !costly requests are much more important than __GFP_REPEAT
-	 * costly ones because they are de facto nofail and invoke OOM
-	 * killer to move on while costly can fail and users are ready
-	 * to cope with that. 1/4 retries is rather arbitrary but we
-	 * would need much more detailed feedback from compaction to
-	 * make a better decision.
-	 */
-	if (order > PAGE_ALLOC_COSTLY_ORDER)
-		max_retries /= 4;
-	if (compaction_retries <= max_retries)
-		return true;
-
-	return false;
-}
 #else
 static inline struct page *
 __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
@@ -3195,6 +3147,8 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 	return NULL;
 }
 
+#endif /* CONFIG_COMPACTION */
+
 static inline bool
 should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_flags,
 		     enum compact_result compact_result,
@@ -3221,7 +3175,6 @@ should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_fla
 	}
 	return false;
 }
-#endif /* CONFIG_COMPACTION */
 
 /* Perform direct synchronous page reclaim */
 static int
-- 
2.8.1


-- 
Michal Hocko
SUSE Labs