linux-kernel - Re: OOM detection regressions since 4.7

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Message-ID: <20160822112036.GA305@x4>
Date:   Mon, 22 Aug 2016 13:20:36 +0200
From:   Markus Trippelsdorf <markus@...ppelsdorf.de>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, greg@...e.cz,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Arkadiusz Miskiewicz <a.miskiewicz@...il.com>,
        Ralf-Peter Rohbeck <Ralf-Peter.Rohbeck@...ntum.com>,
        Jiri Slaby <jslaby@...e.com>, Olaf Hering <olaf@...fle.de>,
        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 2016.08.22 at 13:13 +0200, Michal Hocko wrote:
> On Mon 22-08-16 13:01:13, Markus Trippelsdorf wrote:
> > On 2016.08.22 at 12:56 +0200, Michal Hocko wrote:
> > > On Mon 22-08-16 12:16:14, Markus Trippelsdorf wrote:
> > > > On 2016.08.22 at 11:32 +0200, Michal Hocko wrote:
> > > > > [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?
> > 
> > I don't recall. Must have been some issue in the past. I will re-enable
> > the option.
> 
> Well, without the compaction there is no source of high order pages at
> all. You can only reclaim and hope that some of the reclaimed pages will
> find its buddy on the list and form the higher order page. This can take
> for ever. We used to have the lumpy reclaim and that could help but this
> is long gone.
> 
> I do not think we can really sanely optimize for high-order heavy loads
> without COMPACTION sanely. At least not without reintroducing lumpy
> reclaim or something similar. To be honest I am even not sure which
> configurations should disable compaction - except for really highly
> controlled !mmu or other one purpose systems.

I now recall. It was an issue with CONFIG_TRANSPARENT_HUGEPAGE, so I
disabled that option. This then de-selected CONFIG_COMPACTION...

-- 
Markus