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

[KAMEZAWA Hiroyuki]

On Wed, 21 Jan 2009 12:49:50 -0800 (PST)
David Rientjes <rientjes at 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

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