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

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Date:	Thu, 22 Jan 2009 14:53:13 +0530
From:	Nikanth Karthikesan <knikanth@...e.de>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Evgeniy Polyakov <zbr@...emap.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Snook <csnook@...hat.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Paul Menage <menage@...gle.com>,
	containers@...ts.linux-foundation.org
Subject: Re: [RFC] [PATCH] Cgroup based OOM killer controller

On Thursday 22 January 2009 14:13:38 David Rientjes wrote:
> On Thu, 22 Jan 2009, Nikanth Karthikesan wrote:
> > No, this is not specific to memcg or cpuset cases alone. The same
> > needless kills will take place even without memcg or cpuset when an
> > administrator specifies a light memory consumer to be killed before a
> > heavy memory user. But it is up to the administrator to use it wisely.
>
> You can't specify different behavior for an oom cgroup depending on what
> type of oom it is, which is the problem with this proposal.
>

No. This does not disable any such special selection criteria which is used 
without this controller.

> For example, if your task triggers an oom as the result of its exclusive
> cpuset placement, the oom killer should prefer to kill a task within that
> cpuset to allow for future memory freeing.
>
> So, with your proposal, an administrator can specify the oom priority of
> an entire aggregate of tasks but the behavior may not be desired for a
> cpuset-constrained oom, while it may be perfectly legitimate for a global
> unconstrained oom.
>
> I can specify a higher oom priority for a cpuset because its jobs are less
> critical and I would prefer it gets killed in a system-wide oom, but any
> other cpuset that ooms will needlessly kill these tasks when there is no
> benefit.
>

This patch just chooses the task with highest oom.victim among those tasks 
which would have been chosen without this controller. So all the "kill within 
memcg/cpuset" should work as always! It should just kill a task within the 
memcg with highest oom.victim.

Thanks
Nikanth
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