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Date: Wed, 13 May 2009 10:47:36 -0400
From: Rik van Riel <riel@redhat.com>
Organization: Red Hat, Inc
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To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
CC: LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Christoph Lameter <cl@linux-foundation.org>
Subject: Re: [PATCH 4/4] zone_reclaim_mode is always 0 by default
References: <20090513120155.5879.A69D9226@jp.fujitsu.com> <20090513120729.5885.A69D9226@jp.fujitsu.com>
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KOSAKI Motohiro wrote:
> Subject: [PATCH] zone_reclaim_mode is always 0 by default
> 
> Current linux policy is, if the machine has large remote node distance,
>  zone_reclaim_mode is enabled by default because we've be able to assume to 
> large distance mean large server until recently.
> 
> Unfrotunately, recent modern x86 CPU (e.g. Core i7, Opeteron) have P2P transport
> memory controller. IOW it's NUMA from software view.
> 
> Some Core i7 machine has large remote node distance and zone_reclaim don't
> fit desktop and small file server. it cause performance degression.
> 
> Thus, zone_reclaim == 0 is better by default. sorry, HPC gusy. 
> you need to turn zone_reclaim_mode on manually now.

I'll believe that it causes a performance regression with the
old zone_reclaim behaviour, however the way you tweaked
zone_reclaim should make it behave a lot better, no?

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