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

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Message-Id: <20100616104036.b45d352b.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 16 Jun 2010 10:40:36 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Rik van Riel <riel@...hat.com>
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>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim

On Tue, 15 Jun 2010 20:53:43 -0400
Rik van Riel <riel@...hat.com> wrote:

> On 06/15/2010 08:39 PM, KAMEZAWA Hiroyuki wrote:
> 
> > Hmm, or do you recommend no-dirty-page-writeback when a memcg hits limit ?
> > Maybe we'll see much swaps.
> >
> > I want to go with this for a while, changing memcg's behavior will took
> > some amounts of time, there are only a few developpers.
> 
> One thing we can do, for kswapd, memcg and direct reclaim alike,
> is to tell the flusher threads to flush pages related to a pageout
> candidate page to disk.
> 
> That way the reclaiming processes can wait on some disk IO to
> finish, while the flusher thread takes care of the actual flushing.
> 
> That should also fix the "kswapd filesystem IO has really poor IO
> patterns" issue.
> 
> There's no reason not to fix this issue the right way.
> 
yes. but this patch just stops writeback. I think it's sane to ask
not to change behavior until there are some useful changes in flusher
threads.

IMO, until flusher threads can work with I/O cgroup, memcg shoudln't
depend on it because writeback allows stealing resource without it.

Thanks,
-Kame

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