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 16:46:52 -0700
From:	Vaibhav Nagarnaik <vnagarnaik@...gle.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	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 Fri, May 27, 2011 at 6:50 PM, Steven Rostedt <rostedt@...dmis.org> 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.
>
> -- Steve

You are right. Changing the value of oom_killer_disabled is setting
kernel policy and I don't like the solution either.

It would be great if the user always sets oom_score_adj while
allocating ring buffer memory, but there are different use cases I see
where it might not be feasible. One is the number of different
applications which use ftrace and set the ring buffer memory size
(trace-cmd, perf, powertop, etc). The other case is where a developer
is setting the size for his own tracing. In all these cases,
oom_score_adj *should* be set to maximum to be safe, but it a
developer might forget this step and can de-stabilize the system. This
is why I think that setting oom_score_adj to maximum in the kernel
while allocating buffer as well as using __GFP_NORETRY should suffice
for the end goal of being a good memory citizen.

Vaibhav Nagarnaik
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