linux-kernel - Re: [RFC] [PATCH] Cgroup based OOM killer controller

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Date:	Wed, 21 Jan 2009 22:29:20 -0800
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Nikanth Karthikesan <knikanth@...e.de>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Evgeniy Polyakov <zbr@...emap.net>,
	Chris Snook <csnook@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Paul Menage <menage@...gle.com>,
	containers@...ts.linux-foundation.org
Subject: Re: [RFC] [PATCH] Cgroup based OOM killer controller

On Wed, Jan 21, 2009 at 10:12 PM, Nikanth Karthikesan <knikanth@...e.de> wrote:
> On Thursday 22 January 2009 11:09:45 Arve Hjønnevåg wrote:
>> On Wed, Jan 21, 2009 at 9:13 PM, Nikanth Karthikesan <knikanth@...e.de>
> wrote:
>> > To use oom_adj effectively one should continuously monitor oom_score of
>> > all the processes, which is a complex moving target and keep on adjusting
>> > the oom_adj of many tasks which still cannot guarantee the order. This
>> > controller is deterministic and hence easier to use.
>>
>> Why not add an option to make oom_adj ensure strict ordering instead?
>
> This could be done in 2 ways.
> 1. Make oom_adj itself strict.(based on some other parameter?)
> - Adds to confusion whether the current oom_adj is a strict value or the usual
> suggestion.
> - It would disable the oom_adj suggestion which could have been used till now.
> - It is a public interface, and changing that might break some one's script.
>
> 2. Add addtional parameter, say  /proc/<pid>/oom_order
> - Not easy to use.
> - Say I had assigned the oom.victim to a task and it had forked a lot. Now to
> change the value for all the tasks it is easier with cgroups.
> - Some optimization that Kame specified earlier would be harder to achieve.
>

Both options would work for us, but option 1 require no change to our
user space code. I agree that some operations are easier with a
cgroups approach, but since we don't perform these operations it would
be nice to not require cgroups to control the oom killer.

-- 
Arve Hjønnevåg
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