linux-kernel - Re: [PATCH 9/9] oom: give the dying task a higher priority

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Message-ID: <20100616195447.GH5009@uudg.org>
Date:	Wed, 16 Jun 2010 16:54:47 -0300
From:	"Luis Claudio R. Goncalves" <lclaudio@...g.org>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 9/9] oom: give the dying task a higher priority

On Thu, Jun 17, 2010 at 12:31:20AM +0900, Minchan Kim wrote:
| >         /*
| >          * We give our sacrificial lamb high priority and access to
| >          * all the memory it needs. That way it should be able to
| >          * exit() and clear out its resources quickly...
| >          */
| >  	p->rt.time_slice = HZ;
| >  	set_tsk_thread_flag(p, TIF_MEMDIE);
...
| > +	if (rt_task(p)) {
| > +		p->rt.time_slice = HZ;
| > +		return;

I am not sure the code above will have any real effect for an RT task.
Kosaki-san, was this change motivated by test results or was it just a code
cleanup? I ask that out of curiosity.

| I have a question from long time ago. 
| If we change rt.time_slice _without_ setscheduler, is it effective?
| I mean scheduler pick up the task faster than other normal task?

$ git log --pretty=oneline -Stime_slice mm/oom_kill.c
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 Linux-2.6.12-rc2

This code ("time_slice = HZ;") is around for quite a while and
probably comes from a time where having a big time slice was enough to be
sure you would be the next on the line. I would say sched_setscheduler is
indeed necessary.

Regards,
Luis
-- 
[ Luis Claudio R. Goncalves             Red Hat  -  Realtime Team ]
[ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]

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