linux-kernel - Re: [RFC] oom-kill: give the dying task a higher priority

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Date:	Fri, 28 May 2010 23:06:23 +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 09:53:05AM -0300, Luis Claudio R. Goncalves wrote:
> On Fri, May 28, 2010 at 02:59:02PM +0900, KOSAKI Motohiro wrote:
> | > RT Task
> | > 
> | > void non-RT-function()
> | > {
> | >    system call();
> | >    buffer = malloc();
> | >    memset(buffer);
> | > }
> | > /*
> | >  * We make sure this function must be executed in some millisecond
> | >  */
> | > void RT-function()
> | > {
> | >    some calculation(); <- This doesn't have no dynamic characteristic
> | > }
> | > int main()
> | > {
> | >    non-RT-function();
> | >    /* This function make sure RT-function cannot preempt by others */
> | >    set_RT_max_high_priority();
> | >    RT-function A();
> | >    set_normal_priority();
> | >    non-RT-function();
> | > }
> | > 
> | > We don't want realtime in whole function of the task. What we want is
> | > just RT-function A.
> | > Of course, current Linux cannot make perfectly sure RT-functionA can
> | > not preempt by others.
> | > That's because some interrupt or exception happen. But RT-function A
> | > doesn't related to any dynamic characteristic. What can justify to
> | > preempt RT-function A by other processes?
> | 
> | 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. 

Isn't it enough?
-- 
Kind regards,
Minchan Kim
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