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

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Message-Id: <20100927110628.9bc97ea7.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 27 Sep 2010 11:06:28 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	robm@...tmail.fm, linux-kernel@...r.kernel.org,
	"Bron Gondwana" <brong@...tmail.fm>, linux-mm <linux-mm@...ck.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>
Subject: Re: Default zone_reclaim_mode = 1 on NUMA kernel is bad for
 file/email/web servers

On Mon, 27 Sep 2010 11:04:54 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> > On Thu, 16 Sep 2010 19:01:32 +0900 (JST)
> > KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> > 
> > > Yes, sadly intel motherboard turn on zone_reclaim_mode by default. and
> > > current zone_reclaim_mode doesn't fit file/web server usecase ;-)
> > > 
> > > So, I've created new proof concept patch. This doesn't disable zone_reclaim
> > > at all. Instead, distinguish for file cache and for anon allocation and
> > > only file cache doesn't use zone-reclaim.
> > > 
> > > That said, high-end hpc user often turn on cpuset.memory_spread_page and
> > > they avoid this issue. But, why don't we consider avoid it by default?
> > > 
> > > 
> > > Rob, I wonder if following patch help you. Could you please try it?
> > > 
> > > 
> > > Subject: [RFC] vmscan: file cache doesn't use zone_reclaim by default
> > > 
> > 
> > Hm, can't we use migration of file caches rather than pageout in
> > zone_reclaim_mode ? Doent' it fix anything ?
> 
> Doesn't.
> 
> Two problem. 1) Migration makes copy. then it's slower than zone_reclaim=0
> 2) Migration is only effective if target node has much free pages. but it
> is not generic assumption.
> 
> For this case, zone_reclaim_mode=0 is best. my patch works as second best.
> your one works as third.
> 

Hmm. I'm not sure whether it's "slower" or not. And Migraion doesn't
assume target node because it can use zonelist fallback.

I'm just has concerns that kicked-out pages will be paged-in soon.

But ok, maybe complicated.

Thanks,
-Kame

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