linux-kernel - Re: oom-killer with 27G free swap and overcommit

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Date:	Tue, 28 Aug 2007 11:53:57 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	"Patrick J. LoPresti" <lopresti@...il.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: oom-killer with 27G free swap and overcommit_memory=2

Patrick J. LoPresti wrote:
> I am using Linux 2.6.16.46-0.12-smp (SUSE 10 SP1 stock kernel).
> I do intend to bother SUSE, but I am hoping some kind kernel savant
> can help me interpret these log messages and/or give me some
> suggestions for how to proceed.
> 
> My system is a SunFire x4100 (x86_64) with 16G of RAM and 32G of swap
> in a single partition.  I have an application which consumes a lot of
> memory, and after a few hours the oom-killer kills it.
> 
> This would not be surprising, except a) the machine still has 27G of
> free swap at the time; and b) it happens even when I set
> vm.overcommit_memory=2 (with overcommit_ratio=50).  It is
> time-consuming to reproduce, but consistent.
> 
> Below is the first batch of messages from the oom-killer.  In this
> case, overcommit_memory was set to 2, and the application
> received no failures from malloc() or new.
> 
> 9-10 more such batches appear in the log in rapid succession before
> I get the "Kill process XXXX ... Killed process XXXX" pair of messages.
> 
> Here are my questions.  I realize these log messages may be insufficient
> to answer them, and I am ready to provide more information upon
> request.  (Unfortunately I cannot provide the application itself.  But
> I can perform tests and provide logs.)
> 
> 1) Does this behavior definitely indicate a kernel bug?  If not, what
> could my application possibly be doing to cause it?
> 
> 2) Is there any sysctl setting that might "avoid" this problem?  Or a
> way to change my application to avoid it?
> 
> 3) Should I attempt to reproduce this problem on the stock kernel.org
> kernel?

Hi,

Yeah it doesn't seem like the right behaviour. Your app isn't allocating
mlocked memory, is it? What is the value of your /proc/sys/vm/swappiness
sysctl? (increasing it may help).

I'll take a look at the SLES kernel and see whether we can do better
there. Thanks.

Nick

-- 
SUSE Labs, Novell Inc.
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