linux-kernel - Re: [PATCH 0/3] OOM detection rework v4

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Message-ID: <20160302123752.GE26686@dhcp22.suse.cz>
Date:	Wed, 2 Mar 2016 13:37:53 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Vlastimil Babka <vbabka@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Hillf Danton <hillf.zj@...baba-inc.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] OOM detection rework v4

On Wed 02-03-16 11:55:07, Joonsoo Kim wrote:
> On Tue, Mar 01, 2016 at 07:14:08PM +0100, Vlastimil Babka wrote:
[...]
> > Yes, compaction is historically quite careful to avoid making low
> > memory conditions worse, and to prevent work if it doesn't look like
> > it can ultimately succeed the allocation (so having not enough base
> > pages means that compacting them is considered pointless). This
> > aspect of preventing non-zero-order OOMs is somewhat unexpected :)
> 
> It's better not to assume that compaction would succeed all the times.
> Compaction has some limitations so it sometimes fails.
> For example, in lowmem situation, it only scans small parts of memory
> and if that part is fragmented by non-movable page, compaction would fail.
> And, compaction would defer requests 64 times at maximum if successive
> compaction failure happens before.
> 
> Depending on compaction heavily is right direction to go but I think
> that it's not ready for now. More reclaim would relieve problem.

I really fail to see why. The reclaimable memory can be migrated as
well, no? Relying on the order-0 reclaim makes only sense to get over
wmarks.

-- 
Michal Hocko
SUSE Labs