linux-kernel - Re: [PATCH 2/5] Revert "oom: give the dying task a higher priority"

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Message-ID: <1301318293.4859.19.camel@twins>
Date:	Mon, 28 Mar 2011 15:18:13 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	"Luis Claudio R. Goncalves" <lclaudio@...g.org>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-mm <linux-mm@...ck.org>,
	Andrey Vagin <avagin@...nvz.org>,
	Hugh Dickins <hughd@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 2/5] Revert "oom: give the dying task a higher priority"

On Mon, 2011-03-28 at 10:10 -0300, Luis Claudio R. Goncalves wrote:
> | There was meaningless code in there. I guess it was in there from CFS.
> | Thanks for the explanation, Peter.
> 
> Yes, it was CFS related:
> 
>         p = find_lock_task_mm(p);
>         ...
>         p->rt.time_slice = HZ; <<---- THIS

CFS has never used rt.time_slice, that's always been a pure SCHED_RR
thing.

> Peter, would that be effective to boost the priority of the dying task?

The thing you're currently doing, making it SCHED_FIFO ?

> I mean, in the context of SCHED_OTHER tasks would it really help the dying
> task to be scheduled sooner to release its resources? 

That very much depends on how all this stuff works, I guess if everybody
serializes on OOM and only the first will actually kill a task and all
the waiting tasks will try to allocate a page again before also doing
the OOM thing, and the pending tasks are woken after the OOM target task
has completed dying.. then I don't see much point in boosting things,
since everybody interested in memory will block and eventually only the
dying task will be left running.

Its been a very long while since I stared at the OOM code..

> If so, as we remove
> the code in commit 93b43fa5508 we should re-add that old code. 

It doesn't make any sense to fiddle with rt.time_slice afaict.
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