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

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Date:	Tue, 21 Sep 2010 09:14:13 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Mel Gorman <mel@....ul.ie>
cc:	Rob Mueller <robm@...tmail.fm>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	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 Tue, 21 Sep 2010, Mel Gorman wrote:

> > However there's still another question, why is this problem happening at
> > all for us? I know almost nothing about NUMA, but from other posts, it
> > sounds like the problem is the memory allocations are all happening on
> > one node?
>
> Yes.

This could be a screwy hardware issue as pointed out before. Certain
controllers restrict the memory that I/O can be done to also (32 bit
controller only able to do I/O to lower 2G?, controller on a PCI bus that
is local only to a particular node) which would make balancing
the file cache difficult.
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