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

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Message-Id: <1284708756.2702.1395472601@webmail.messagingengine.com>
Date:	Fri, 17 Sep 2010 17:32:36 +1000
From:	"Robert Mueller" <robm@...tmail.fm>
To:	"Shaohua Li" <shaohua.li@...el.com>
Cc:	"Christoph Lameter" <cl@...ux.com>,
	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Bron Gondwana" <brong@...tmail.fm>,
	"linux-mm" <linux-mm@...ck.org>, "Mel Gorman" <mel@....ul.ie>
Subject: Re: Default zone_reclaim_mode = 1 on NUMA kernel is bad for
 file/email/web servers

> > I don't think this is any fault of how the software works. It's a
> > *very* standard "pre-fork child processes, allocate incoming
> > connections to a child process, open and mmap one or more files to
> > read data from them". That's not exactly a weird programming model,
> > and it's bad that the kernel is handling that case very badly with
> > everything default.
>
> maybe you incoming connection always happen on one CPU and you do the
> page allocation in that cpu, so some nodes use out of memory but
> others have a lot free. Try bind the child process to different nodes
> might help.

There's are 5000+ child processes (it's a cyrus IMAP server). Neither
the parent of any of the children are bound to any particular CPU. It
uses a standard fcntl lock to make sure only one spare child at a time
calls accept(). I don't think that's the problem.

Rob
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