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

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Date:	Fri, 28 May 2010 14:30:49 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	balbir@...ux.vnet.ibm.com,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	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

Hi, Kosaki.

On Fri, May 28, 2010 at 1:46 PM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> * Luis Claudio R. Goncalves <lclaudio@...g.org> [2010-05-28 00:51:47]:
>>
>> > @@ -382,6 +382,8 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
>> >   */
>> >  static void __oom_kill_task(struct task_struct *p, int verbose)
>> >  {
>> > +   struct sched_param param;
>> > +
>> >     if (is_global_init(p)) {
>> >             WARN_ON(1);
>> >             printk(KERN_WARNING "tried to kill init!\n");
>> > @@ -413,8 +415,9 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>> >      */
>> >     p->rt.time_slice = HZ;
>> >     set_tsk_thread_flag(p, TIF_MEMDIE);
>> > -
>> >     force_sig(SIGKILL, p);
>> > +   param.sched_priority = MAX_RT_PRIO-1;
>> > +   sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
>> >  }
>> >
>>
>> I would like to understand the visible benefits of this patch. Have
>> you seen an OOM kill tasked really get bogged down. Should this task
>> really be competing with other important tasks for run time?
>
> What you mean important? Until OOM victim task exit completely, the system have no memory.
> all of important task can't do anything.
>
> In almost kernel subsystems, automatically priority boost is really bad idea because
> it may break RT task's deterministic behavior. but OOM is one of exception. The deterministic
> was alread broken by memory starvation.

Yes or No.

IMHO, normally RT tasks shouldn't use dynamic allocation(ie,
non-deterministic functions or system calls) in place which is needed
deterministic. So memory starvation might not break real-time
deterministic.


>
> That's the reason I acked it.

>
>
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-- 
Kind regards,
Minchan Kim
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