Re: OOM detection regressions since 4.7

From: Michal Hocko <mhocko@kernel.org>
To: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	greg@suse.cz, Linus Torvalds <torvalds@linux-foundation.org>,
	Arkadiusz Miskiewicz <a.miskiewicz@gmail.com>,
	Ralf-Peter Rohbeck <Ralf-Peter.Rohbeck@quantum.com>,
	Jiri Slaby <jslaby@suse.com>, Olaf Hering <olaf@aepfle.de>,
	Vlastimil Babka <vbabka@suse.cz>, Joonsoo Kim <js1304@gmail.com>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: OOM detection regressions since 4.7
Date: Mon, 22 Aug 2016 12:56:53 +0200	[thread overview]
Message-ID: <20160822105653.GI13596@dhcp22.suse.cz> (raw)
In-Reply-To: <20160822101614.GA314@x4>

On Mon 22-08-16 12:16:14, Markus Trippelsdorf wrote:
> On 2016.08.22 at 11:32 +0200, Michal Hocko wrote:
> > there have been multiple reports [1][2][3][4][5] about pre-mature OOM
> > killer invocations since 4.7 which contains oom detection rework. All of
> > them were for order-2 (kernel stack) alloaction requests failing because
> > of a high fragmentation and compaction failing to make any forward
> > progress. While investigating this we have found out that the compaction
> > just gives up too early. Vlastimil has been working on compaction
> > improvement for quite some time and his series [6] is already sitting
> > in mmotm tree. This already helps a lot because it drops some heuristics
> > which are more aimed at lower latencies for high orders rather than
> > reliability. Joonsoo has then identified further problem with too many
> > blocks being marked as unmovable [7] and Vlastimil has prepared a patch
> > on top of his series [8] which is also in the mmotm tree now.
> > 
> > That being said, the regression is real and should be fixed for 4.7
> > stable users. [6][8] was reported to help and ooms are no longer
> > reproducible. I know we are quite late (rc3) in 4.8 but I would vote
> > for mergeing those patches and have them in 4.8. For 4.7 I would go
> > with a partial revert of the detection rework for high order requests
> > (see patch below). This patch is really trivial. If those compaction
> > improvements are just too large for 4.8 then we can use the same patch
> > as for 4.7 stable for now and revert it in 4.9 after compaction changes
> > are merged.
> > 
> > Thoughts?
> > 
> > [1] http://lkml.kernel.org/r/20160731051121.GB307@x4
> 
> For the report [1] above:
> 
> markus@x4 linux % cat .config | grep CONFIG_COMPACTION
> # CONFIG_COMPACTION is not set

Hmm, without compaction and a heavy fragmentation then I am afraid we
cannot really do much. What is the reason to disable compaction in the
first place?
-- 
Michal Hocko
SUSE Labs

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