Re: [RFC] [PATCH] Cgroup based OOM killer controller

KAMEZAWA Hiroyuki
2009-01-22T05:28:41Z

On Thu, 22 Jan 2009 10:43:12 +0530
Nikanth Karthikesan <knikanth@suse.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@suse.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@suse.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