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

KAMEZAWA Hiroyuki
2009-01-22T02:54:41Z

On Wed, 21 Jan 2009 12:49:50 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> On Wed, 21 Jan 2009, Nikanth Karthikesan wrote:
>
> > 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.
> >
>
> This doesn't help in memcg or cpuset constrained oom conditions, which
> still go through select_bad_process().
>
> If the oom.victim value is high for a specific cgroup and a memory
> controller oom occurs in a disjoint cgroup, for example, it's possible to
> needlessly kill tasks. Obviously that is up to the administrator to
> configure, but may not be his or her desire for system-wide oom
> conditions.
>
Hmm...after this patch, select_bad_process's filter to select process will be

==
1. ->mm is NULL ? => don't select this
2. is init task ? => don't select this
3. is under specified memcg ? => don't select this
4. marked as MEMDIE ? => return -1.
5. PF_EXITING? => select this.
6. OOM_DISABLE ? => don't select this
points = badness(p, uptime.tv_sec);
7. adjust point & select logic depends on OOM cgroup
==

Not looks good ;)

> It may be preferred to kill tasks in a specific cgroup first when the
> entire system is out of memory or kill tasks within a cgroup attached to a
> memory controller when it is oom.
>

I agree here.

Above filter logic should be
==
current_victim_level++;
1. p is under oom cgroup of victim_level > current_victim_level => don't select this.
2. ->mm is NULL ? => don't select this
3. is init task ? => don't select this
4. is under specified memcg ? => don't select this
5. marked as MEMDIE ? => return -1.
6. PF_EXITING? => select this.
7. OOM_DISABLE ? => don't select this
points = badness(p, uptime.tv_sec)
==
But this will be too slow.

I think do_each_thread() in select_bad_process() should be replaced with
a routine like this, finally.
==
for_each_oom_cgroup_in_victim_value_order() {
for_each_threads_in_oom_cgroup(oom) {
select one bad thread.
}
if (selected_one_is_enough_bad ?)
return selected_one;
}
==

And this can be a help for "spped up OOM killer" problem.

Thanks,
-Kame