linux-kernel - Re: [PATCH] trace: Set oom_score_adj to maximum for ring buffer allocating process

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Date:	Mon, 30 May 2011 16:54:01 -0700
From:	Vaibhav Nagarnaik <vnagarnaik@...gle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	David Rientjes <rientjes@...gle.com>,
	Ingo Molnar <mingo@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Michael Rubin <mrubin@...gle.com>,
	David Sharp <dhsharp@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] trace: Set oom_score_adj to maximum for ring buffer
 allocating process

On Sun, May 29, 2011 at 11:23 PM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
> (2011/05/28 10:50), Steven Rostedt wrote:
>> On Fri, 2011-05-27 at 17:44 -0700, Vaibhav Nagarnaik wrote:
>>
>>> That said, I am open to changing it if Steven and you think using
>>> oom_killer_disabled is a better solution.
>>
>> My biggest concern is that we are setting policy in the kernel. If you
>> are concerned about this, why not just have the process that is going to
>> increase the size of the ring buffer adjust its own oom policy
>> with /proc/<pid>/oom_score_adj ? Only a privilege process can increase
>> the size of the ring buffer so it's not like we are worried about any
>> normal user task upping the ring buffer to kill other processes.
>
> I like Steven's approach.
>
> Because even if we apply Vaibhav's patch, we still have a oom issue.
> because when oom-killer killed echo commands, it doesn't shrink ring
> buffer. it only just die. So, the kernel is still under extreme memory
> shortage. Any admins operation may invoke next oom-killer.

The ring buffer allocation is done synchronously with the echo
command. When a process is picked by the OOM killer, it has a fatal
signal pending. Any further allocations by the process in that
scenario will return with a failure. The ring buffer allocation code
can handle this scenario very well and give up all the previously
allocated memory.



Vaibhav Nagarnaik
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