linux-kernel - Re: Kernel 2.6.29 runs out of memory and hangs.

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Date:	Fri, 24 Apr 2009 21:16:48 +0200
From:	Zeno Davatz <zdavatz@...il.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	linux-kernel@...r.kernel.org, Hannes Wyss <hwyss@...see.com>
Subject: Re: Kernel 2.6.29 runs out of memory and hangs.

Dear David

On Fri, Apr 24, 2009 at 9:00 PM, David Rientjes <rientjes@...gle.com> wrote:
> On Fri, 24 Apr 2009, Zeno Davatz wrote:
>
>> Apr 24 09:01:06 thinpower [1349923.693331] Out of memory: kill process
>> 21490 (apache2) score 53801 or a child
>> Apr 24 09:01:06 thinpower [1349923.693410] Killed process 21490 (apache2)
>>
>
> If your machine hangs here, then it's most likely because apache2 is
> getting stuck in D state and cannot exit (and it has access to memory
> reserves because of TIF_MEMDIE since it has been oom killed, so it may
> deplete all memory).
>
> I'm assuming that you're describing a machine hang as the inability to
> ping it or ssh into it, not simply your apache server dying.

Yes correct. I could neither SSH into the machine nor could I type
anything on the screen after I connected the monitor and the keyboard
directly to the machine.

> These types of livelocks are possible with the oom killer when a task
> fails to exit, one possible way to fix that is to introduce an oom killer
> timeout such that if a task fails to exit for a pre-defined period of
> time, the oom killer will choose to kill another task in the hopes of
> future memory freeing.  The problem with that approach, however, is that
> the hung task can consume an enormous amount of memory that will never be
> freed.

Thanks for the hint! Is there another solution as well? Any
Kernel-Upgrades in the Pipeline? What does Linus think about this?

>> > If this is reproducible, I'd recommend enabling
>> > /proc/sys/vm/oom_dump_tasks so that the oom killer will dump the tasklist
>> > and show us what may be causing the livelock.
>>
>> Ok, how do I enable that? I will google for it.
>>
>
> You're right in your reply, you can enable it with
>
>        echo 1 > /proc/sys/vm/oom_dump_tasks
>
> This will print the tasklist and some pertinent information alongside the
> oom killer output you've already posted.  It will give a better idea of
> the memory usage on the machine and if killing a subsequent task would
> actually help in this case.

Ok done that. Actually not looking forward that it hangs again but if
it does we should catch some fish. ;)

Best
Zeno
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