linux-kernel - Re: [RFC PATCH 2/2] Don't continue reclaim if the system have plenty free memory

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Message-Id: <20090709140234.239F.A69D9226@jp.fujitsu.com>
Date:	Thu,  9 Jul 2009 14:08:38 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [RFC PATCH 2/2] Don't continue reclaim if the system have plenty  free memory

> Hi, Kosaki.
> 
> On Tue, Jul 7, 2009 at 6:48 PM, KOSAKI
> Motohiro<kosaki.motohiro@...fujitsu.com> wrote:
> > Subject: [PATCH] Don't continue reclaim if the system have plenty free memory
> >
> > On concurrent reclaim situation, if one reclaimer makes OOM, maybe other
> > reclaimer can stop reclaim because OOM killer makes enough free memory.
> >
> > But current kernel doesn't have its logic. Then, we can face following accidental
> > 2nd OOM scenario.
> >
> > 1. System memory is used by only one big process.
> > 2. memory shortage occur and concurrent reclaim start.
> > 3. One reclaimer makes OOM and OOM killer kill above big process.
> > 4. Almost reclaimable page will be freed.
> > 5. Another reclaimer can't find any reclaimable page because those pages are
> > ? already freed.
> > 6. Then, system makes accidental and unnecessary 2nd OOM killer.
> >
> 
> Did you see the this situation ?
> Why I ask is that we have already a routine for preventing parallel
> OOM killing in __alloc_pages_may_oom.
>
> Couldn't it protect your scenario ?

Can you please see actual code of this patch?
Those two patches fix different problem.

1/2 fixes the issue of that concurrent direct reclaimer makes
too many isolated pages.
2/2 fixes the issue of that reclaim and exit race makes accidental oom.


> If it can't, Could you explain the scenario in more detail ?

__alloc_pages_may_oom() check don't effect the threads of already
entered reclaim. it's obvious.




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