linux-kernel - Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim

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Message-ID: <4C1787DF.3020102@redhat.com>
Date:	Tue, 15 Jun 2010 10:02:07 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Mel Gorman <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim

On 06/15/2010 09:37 AM, Christoph Hellwig wrote:
> On Tue, Jun 15, 2010 at 09:34:18AM -0400, Rik van Riel wrote:
>> If direct reclaim can overflow the stack, so can direct
>> memcg reclaim.  That means this patch does not solve the
>> stack overflow, while admitting that we do need the
>> ability to get specific pages flushed to disk from the
>> pageout code.
>
> Can you explain what the hell memcg reclaim is and why it needs
> to reclaim from random contexts?

The page fault code will call the cgroup accounting code.

When a cgroup goes over its memory limit, __mem_cgroup_try_charge
will call mem_cgroup_hierarchical_reclaim, which will then go
into the page reclaim code.

> It seems everything that has a cg in it's name that I stumbled over
> lately seems to be some ugly wart..

No argument there.  It took me a few minutes to find the code
path above :)

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