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

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Date:	Thu, 22 Jan 2009 14:27:21 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Nikanth Karthikesan <knikanth@...e.de>
Cc:	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>,
	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 Thu, 22 Jan 2009 10:43:12 +0530
Nikanth Karthikesan <knikanth@...e.de> wrote:

> On Thursday 22 January 2009 08:58:43 KAMEZAWA Hiroyuki wrote:
> > On Wed, 21 Jan 2009 16:38:21 +0530
> >
> > Nikanth Karthikesan <knikanth@...e.de> wrote:
> > > As Alan Cox suggested/wondered in this thread,
> > > http://lkml.org/lkml/2009/1/12/235 , this is a container group based
> > > approach to override the oom killer selection without losing all the
> > > benefits of the current oom killer heuristics and oom_adj interface.
> > >
> > > It adds a tunable oom.victim to the oom cgroup. The oom killer will kill
> > > the process using the usual badness value but only within the cgroup with
> > > the maximum value for oom.victim before killing any process from a cgroup
> > > with a lesser oom.victim number. Oom killing could be disabled by setting
> > > oom.victim=0.
> > >
> > > Signed-off-by: Nikanth Karthikesan <knikanth@...e.de>
> >
> > Assume following
> >   - the usar can tell "which process should be killed at first"
> >
> > What is the difference between oom_adj and this cgroup to users ?
> 
> It is next to impossible to specify the order among say 10 memory hogging 
> tasks using oom_adj. Using this oom-controller users can specify the exact 
> order.
> 
> > If oom_adj is hard to use, making it simpler is a good way, I think.
> > rather than adding new complication.
> >
> > It seems both of oom_adj and this cgroup will be hard-to-use functions
> > for usual system administrators. But no better idea than using memcg
> > and committing memory usage.
> >
> 
> 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.
> 

Okay, thank you for explanation :)
I think it's better to explain "why this is much easier to use rather
than oom_adj and what is the benefit to users." in your patch description
and to improve your documentation.

+But it is very difficult to suggest an order among tasks to be killed during
+Out Of Memory situation. The OOM Killer controller aids in doing that.

As.
 Difference from oom_adj:
 This allows users to specify "strict order" of oom-kill's select-bad-process
 operation. While oom_adj just works as a hint for the kernel, OOM Killer
 Controller gives users full control.

 In general, it's very hard to specify oom-kill order of several applications
 only by oom_adj because it's just affects "badness" calculation.

A my English skill is poor, you'll be able to write better text ;)

Regards,
-Kame

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