Date: Thu, 22 Jan 2009 11:53:24 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: David Rientjes <rientjes@google.com>
Cc: Nikanth Karthikesan <knikanth@suse.de>,
       containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
       Arve =?UTF-8?B?SGrDuG5uZXbDpWc=?= <arve@android.com>,
       Evgeniy Polyakov <zbr@ioremap.net>,
       Andrew Morton <akpm@linux-foundation.org>,
       Chris Snook <csnook@redhat.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Paul Menage <menage@google.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: [RFC] [PATCH] Cgroup based OOM killer controller
Message-Id: <20090122115324.b954c6a1.kamezawa.hiroyu@jp.fujitsu.com>
In-Reply-To: <alpine.DEB.2.00.0901211241040.21080@chino.kir.corp.google.com>
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	<20090121131739.GB4997@ioremap.net>
	<200901212054.34929.knikanth@suse.de>
	<alpine.DEB.2.00.0901211241040.21080@chino.kir.corp.google.com>
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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

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