Message-ID: <20100528151249.GB12035@barrios-desktop>
Date:	Sat, 29 May 2010 00:12:49 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	"Luis Claudio R. Goncalves" <lclaudio@...g.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	balbir@...ux.vnet.ibm.com, Oleg Nesterov <oleg@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mel@....ul.ie>, williams@...hat.com
Subject: Re: [RFC] oom-kill: give the dying task a higher priority

On Fri, May 28, 2010 at 11:36:17AM -0300, Luis Claudio R. Goncalves wrote:
> On Fri, May 28, 2010 at 11:06:23PM +0900, Minchan Kim wrote:
> | On Fri, May 28, 2010 at 09:53:05AM -0300, Luis Claudio R. Goncalves wrote:
> | > On Fri, May 28, 2010 at 02:59:02PM +0900, KOSAKI Motohiro wrote:
> ...
> | > | As far as my observation, RT-function always have some syscall. because pure
> | > | calculation doesn't need deterministic guarantee. But _if_ you are really
> | > | using such priority design. I'm ok maximum NonRT priority instead maximum
> | > | RT priority too.
> | > 
> | > I confess I failed to distinguish memcg OOM and system OOM and used "in
> | > case of OOM kill the selected task the faster you can" as the guideline.
> | > If the exit code path is short that shouldn't be a problem.
> | > 
> | > Maybe the right way to go would be giving the dying task the biggest
> | > priority inside that memcg to be sure that it will be the next process from
> | > that memcg to be scheduled. Would that be reasonable?
> | 
> | Hmm. I can't understand your point. 
> | What do you mean failing distinguish memcg and system OOM?
> | 
> | We already have been distinguish it by mem_cgroup_out_of_memory.
> | (but we have to enable CONFIG_CGROUP_MEM_RES_CTLR). 
> | So task selected in select_bad_process is one out of memcg's tasks when 
> | memcg have a memory pressure. 
> 
> The approach of giving the highest priority to the dying task makes sense
> in a system wide OOM situation. I though that would also be good for the
> memcg OOM case.
> 
> After Balbir Singh's comment, I understand that in a memcg OOM the dying
> task should have a priority just above the priority of the main task of
> that memcg, in order to avoid interfering in the rest of the system.
> 
> That is the point where I failed to distinguish between memcg and system OOM.
> 
> Should I pursue that new idea of looking for the right priority inside the
> memcg or is it overkill? I really don't have a clear view of the impact of
> a memcg OOM on system performance - don't know if it is better to solve the
> issue sooner (highest RT priority) or leave it to be solved later (highest
> prio on the memcg). I have the impression the general case points to the
> simpler solution.

I think highest RT proirity ins't good solution.
As I mentiond, Some RT functions don't want to be preempted by other processes
which cause memory pressure. It makes RT task broken.

On the other hand, normal processes don't have a requirement of RT.
But it isn't a big problem that it lost little time slice, I think. 
So how about raising max normal priority? 
but I am not sure this is right solution.
Let's listen other's opinion. 
I believe Peter have a good idea.

> 
> Luis
> -- 
> [ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
> [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]
> 

-- 
Kind regards,
Minchan Kim
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