linux-kernel - Re: [PATCH] slub: Avoid direct compaction if possible

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Message-ID: <0000013f43718d4d-7bb260e7-8115-4891-bb26-6febacb7169d-000000@email.amazonses.com>
Date:	Fri, 14 Jun 2013 16:08:02 +0000
From:	Christoph Lameter <cl@...two.org>
To:	Roman Gushchin <klamm@...dex-team.ru>
cc:	Pekka Enberg <penberg@...nel.org>, mpm@...enic.com,
	akpm@...ux-foundation.org, mgorman@...e.de,
	David Rientjes <rientjes@...gle.com>, glommer@...il.com,
	hannes@...xchg.org, minchan@...nel.org, jiang.liu@...wei.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] slub: Avoid direct compaction if possible

On Fri, 14 Jun 2013, Roman Gushchin wrote:

> But there is an actual problem, that this patch solves.
> Sometimes I saw the following issue on some machines:
> all CPUs are performing compaction, system time is about 80%,
> system is completely unreliable. It occurs only on machines
> with specific workload (distributed data storage system, so,
> intensive disk i/o is performed). A system can fall into
> this state fast and unexpectedly or by progressive degradation.

Well that is not a slab allocator specific issue but related to compaction
concurrency. Likely cache line contention is causing a severe slowday. But
that issue could be triggered by any subsystem that does lots of memory
allocations. I would suggest that we try to address the problem in the
compaction logic rather than modifying allocators.

Mel?
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