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

[Serge Hallyn <serge.hallyn@ubuntu.com>]

Quoting Aaron Staley (aaron@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.

> 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
> _______________________________________________
> Containers mailing list
> Containers@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/containers

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