linux-kernel - Re: [PATCH -mm] throttle direct reclaim when too many pages are isolated already

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Message-ID: <4A5E9A33.3030704@redhat.com>
Date:	Wed, 15 Jul 2009 23:10:43 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [PATCH -mm] throttle direct reclaim when too many pages are isolated
 already

Andrew Morton wrote:
> On Wed, 15 Jul 2009 22:38:53 -0400 Rik van Riel <riel@...hat.com> wrote:
> 
>> When way too many processes go into direct reclaim, it is possible
>> for all of the pages to be taken off the LRU.  One result of this
>> is that the next process in the page reclaim code thinks there are
>> no reclaimable pages left and triggers an out of memory kill.
>>
>> One solution to this problem is to never let so many processes into
>> the page reclaim path that the entire LRU is emptied.  Limiting the
>> system to only having half of each inactive list isolated for
>> reclaim should be safe.
>>
> 
> Since when?  Linux page reclaim has a bilion machine years testing and
> now stuff like this turns up.  Did we break it or is this a
> never-before-discovered workload?

It's been there for years, in various forms.  It hardly ever
shows up, but Kosaki's patch series give us a nice chance to
fix it for good.

>> @@ -1049,6 +1070,10 @@ static unsigned long shrink_inactive_lis
>>  	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
>>  	int lumpy_reclaim = 0;
>>  
>> +	while (unlikely(too_many_isolated(zone, file))) {
>> +		schedule_timeout_interruptible(HZ/10);
>> +	}
> 
> This (incorrectly-laid-out) code is a no-op if signal_pending().

Good point, I should add some code to break out of page reclaim
if a fatal signal is pending, and use a normal schedule_timeout
otherwise.

Btw, how is this laid out wrong?  How do I do this better?

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