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

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Message-Id: <200901221142.00803.knikanth@suse.de>
Date:	Thu, 22 Jan 2009 11:42:00 +0530
From:	Nikanth Karthikesan <knikanth@...e.de>
To:	Arve Hjønnevåg <arve@...roid.com>
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 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.

Basically oom-controller implements option 2, using cgroups which can be 
thought of as a modern interface for proc. Also it could be used along with 
other cgroup controllers like the group scheduler. Say you have 2 groups of 
tasks, clubed as entertainment and science, you could use the group scheduler 
to give more CPU bandwidth to science and instruct oom-controller to kill 
entertainment tasks in case of OOM situation.

Thanks
Nikanth

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