PROBLEM: Processes writing large files in memory-limited LXC container are killed by OOM

Aaron Staley aaron at picloud.com
Mon Jul 1 18:51:33 UTC 2013


Hi Johannes,

It does appear to still be happening on Linux 3.8.  Does it remain an open
issue?

Regards,
Aaron


On Mon, Jul 1, 2013 at 11:45 AM, Johannes Weiner <hannes at cmpxchg.org> wrote:

> On Mon, Jul 01, 2013 at 01:01:01PM -0500, Serge Hallyn wrote:
> > Quoting Aaron Staley (aaron at picloud.com):
> > > This is better explained here:
> > >
> http://serverfault.com/questions/516074/why-are-applications-in-a-memory-limited-lxc-container-writing-large-files-to-di
> > > (The
> > > highest-voted answer believes this to be a kernel bug.)
> >
> > Hi,
> >
> > in irc it has been suggested that indeed the kernel should be slowing
> > down new page creates while waiting for old page cache entries to be
> > written out to disk, rather than ooming.
> >
> > With a 3.0.27-1-ac100 kernel, doing dd if=/dev/zero of=xxx bs=1M
> > count=100 is immediately killed.  In contrast, doing the same from a
> > 3.0.8 kernel did the right thing for me.  But I did reproduce your
> > experiment below on ec2 with the same result.
> >
> > So, cc:ing linux-mm in the hopes someone can tell us whether this
> > is expected behavior, known mis-behavior, or an unknown bug.
>
> It's a known issue that was fixed/improved in e62e384 'memcg: prevent
> OOM with too many dirty pages', included in 3.6+.
>
> > > Summary: I have set up a system where I am using LXC to create multiple
> > > virtualized containers on my system with limited resources.
> Unfortunately, I'm
> > > running into a troublesome scenario where the OOM killer is hard
> killing
> > > processes in my LXC container when I write a file with size exceeding
> the
> > > memory limitation (set to 300MB). There appears to be some issue with
> the
> > > file buffering respecting the containers memory limit.
> > >
> > >
> > > Reproducing:
> > >
> > > /done on a c1.xlarge instance running on Amazon EC2
> > >
> > > Create 6 empty lxc containers (in my case I did lxc-create -n testcon
> -t
> > > ubuntu -- -r precise)
> > >
> > > Modify the configuration of each container to set lxc.cgroup.memory.
> > > limit_in_bytes = 300M
> > >
> > > Within each container run:
> > > dd if=/dev/zero of=test2 bs=100k count=5010
> > > parallel
> > >
> > > This will with high probability activate the OOM (as seen in demsg);
> often
> > > the dd processes themselves will be killed.
> > >
> > > This has been verified to have problems on:
> > > Linux 3.8.0-25-generic #37-Ubuntu SMP and Linux ip-10-8-139-98
> > > 3.2.0-29-virtual #46-Ubuntu SMP Fri Jul 27 17:23:50 UTC 2012 x86_64
> x86_64
> > > x86_64 GNU/Linux
> > >
> > > Please let me know your thoughts.
> > >
> > > Regards,
> > > Aaron Staley
> > > _______________________________________________
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> >
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>



-- 
Aaron Staley
*PiCloud, Inc.*


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