linux-kernel - Re: The performance and behaviour of the anti-fragmentation related patches

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Date:	Fri, 02 Mar 2007 17:03:10 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Bill Irwin <bill.irwin@...cle.com>,
	Christoph Lameter <clameter@...r.sgi.com>,
	Mel Gorman <mel@...net.ie>, npiggin@...e.de, mingo@...e.hu,
	jschopp@...tin.ibm.com, arjan@...radead.org,
	torvalds@...ux-foundation.org, mbligh@...igh.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: The performance and behaviour of the anti-fragmentation related
 patches

Andrew Morton wrote:
> On Fri, 02 Mar 2007 16:19:19 -0500
> Rik van Riel <riel@...hat.com> wrote:
>> Bill Irwin wrote:
>>> On Fri, Mar 02, 2007 at 01:23:28PM -0500, Rik van Riel wrote:
>>>> With 32 CPUs diving into the page reclaim simultaneously,
>>>> each trying to scan a fraction of memory, this is disastrous
>>>> for performance.  A 256GB system should be even worse.
>>> Thundering herds of a sort pounding the LRU locks from direct reclaim
>>> have set off the NMI oopser for users here.
>> Ditto here.
> 
> Opterons?

It's happened on IA64, too.  Probably on Intel x86-64 as well.

>> The main reason they end up pounding the LRU locks is the
>> swappiness heuristic.  They scan too much before deciding
>> that it would be a good idea to actually swap something
>> out, and with 32 CPUs doing such scanning simultaneously...
> 
> What kernel version?

Customers are on the 2.6.9 based RHEL4 kernel, but I believe
we have reproduced the problem on 2.6.18 too during stress
tests.

I have no reason to believe we should stick our heads in the
sand and pretend it no longer exists on 2.6.21.

-- 
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is.  Each group
calls the other unpatriotic.
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