linux-kernel - Re: Unending loop in __alloc_pages_slowpath following OOM-kill; rfc: patch.

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Date:	Tue, 24 May 2011 10:16:11 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	minchan.kim@...il.com, abarry@...y.com, akpm@...ux-foundation.org,
	linux-mm@...ck.org, riel@...hat.com, hannes@...xchg.org,
	linux-kernel@...r.kernel.org
Subject: Re: Unending loop in __alloc_pages_slowpath following OOM-kill; rfc:
 patch.

On Tue, May 24, 2011 at 06:05:59PM +0900, KOSAKI Motohiro wrote:
> >>> Why?
> >>
> >> Otherwise, we don't have good PCP dropping trigger. Big machine might have
> >> big pcp cache.
> >>
> > 
> > Big machines also have a large cost for sending IPIs.
> 
> Yes. But it's only matter if IPIs are frequently happen.
> But, drain_all_pages() is NOT only IPI source. some vmscan function (e.g.
> try_to_umap) makes a lot of IPIs.
> 
> Then, it's _relatively_ not costly. I have a question. Do you compare which
> operation and drain_all_pages()? IOW, your "costly" mean which scenario suspect?
> 

I am concerned that if the machine gets into trouble and we are failing
to reclaim that sending more IPIs is not going to help any. There is no
evidence at the moment that sending extra IPIs here will help anything.

-- 
Mel Gorman
SUSE Labs
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