linux-kernel - Re: Default zone_reclaim_mode = 1 on NUMA kernel is bad forfile/email/web servers

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Message-ID: <alpine.DEB.2.00.1010040805500.2502@router.home>
Date:	Mon, 4 Oct 2010 08:07:42 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	Mel Gorman <mel@....ul.ie>, Rob Mueller <robm@...tmail.fm>,
	linux-kernel@...r.kernel.org, Bron Gondwana <brong@...tmail.fm>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: Default zone_reclaim_mode = 1 on NUMA kernel is bad forfile/email/web
 servers

On Mon, 4 Oct 2010, KOSAKI Motohiro wrote:

> > The problem with zone reclaim mainly is created for large apps whose
> > working set is larger than the local node. The special settings are only
> > needing for those applications.
>
> In theory, yes. but please talk with userland developers. They always say
> "Our software work fine on *BSD, Solaris, Mac, etc etc. that's definitely
> linux problem". /me have no way to persuade them ;-)

Do those support NUMA? I would think not. You would have to switch on
interleave at the BIOS level (getting a hardware hack in place to get
rid of the NUMA effects) to make these OSes run right.

> This is one of option. but we don't need to create x86 arch specific
> RECLAIM_DISTANCE. Because practical high-end numa machine are either
> ia64(SGI, Fujitsu) or Power(IBM) and both platform already have arch
> specific definition. then changing RECLAIM_DISTANCE doesn't make any
> side effect on such platform. and if possible, x86 shouldn't have
> arch specific definition because almost minor arch don't have a lot of
> tester and its quality often depend on testing on x86.
>
> attached a patch below.

Looks good.

Acked-by: Christoph Lameter <cl@...ux.com>

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