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

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Date:	Mon, 31 May 2010 00:09:00 +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 01:48:26PM -0300, Luis Claudio R. Goncalves wrote:
> On Sat, May 29, 2010 at 12:45:49AM +0900, Minchan Kim wrote:
> | On Fri, May 28, 2010 at 12:28:42PM -0300, Luis Claudio R. Goncalves wrote:
> | > On Sat, May 29, 2010 at 12:12:49AM +0900, Minchan Kim wrote:
> ...
> | > | 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.
> | > 
> | > For the RT case, if you reached a system OOM situation, your determinism has
> | > already been hurt. If the memcg OOM happens on the same memcg your RT task
> | > is - what will probably be the case most of time - again, the determinism
> | > has deteriorated. For both these cases, giving the dying task SCHED_FIFO
> | > MAX_RT_PRIO-1 means a faster recovery.
> | 
> | What I want to say is that determinisic has no relation with OOM. 
> | Why is some RT task affected by other process's OOM?
> | 
> | Of course, if system has no memory, it is likely to slow down RT task. 
> | But it's just only thought. If some task scheduled just is exit, we don't need
> | to raise OOMed task's priority.
> | 
> | But raising min rt priority on your patch was what I want.
> | It doesn't preempt any RT task.
> | 
> | So until now, I have made noise about your patch.
> | Really, sorry for that. 
> | I don't have any objection on raising priority part from now on. 
> 
> This is the third version of the patch, factoring in your input along with
> Peter's comment. Basically the same patch, but using the lowest RT priority
> to boost the dying task.
> 
> Thanks again for reviewing and commenting.
> Luis
> 
> oom-killer: give the dying task rt priority (v3)
> 
> Give the dying task RT priority so that it can be scheduled quickly and die,
> freeing needed memory.
> 
> Signed-off-by: Luis Claudio R. Gonçalves <lgoncalv@...hat.com>
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 84bbba2..2b0204f 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -266,6 +266,8 @@ static struct task_struct *select_bad_process(unsigned long *ppoints)
>   */
>  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");
> @@ -288,6 +290,8 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
>  	 * exit() and clear out its resources quickly...
>  	 */
>  	p->time_slice = HZ;
> +	param.sched_priority = MAX_RT_PRIO-10;

I can't understand your point, still.
Why you put the priority as "MAX_RT_PRIO - 10"?
What I and peter mentioned was "1" which is lowest RT priority. 

> +	sched_setscheduler(p, SCHED_FIFO, &param);

Why do you change sched_setscheduler_nocheck with sched_set_scheduler?
It means you can't boost prioity if current context doesn't have permission.
Is it a your intention?

>  	set_tsk_thread_flag(p, TIF_MEMDIE);
>  
>  	force_sig(SIGKILL, p);
> -- 
> [ 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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