linux-kernel - Re: [PATCH 11/12] vmscan: Write out dirty pages in batch

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Date:	Mon, 14 Jun 2010 17:13:37 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mel@....ul.ie>
CC:	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>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 11/12] vmscan: Write out dirty pages in batch

On 06/14/2010 07:17 AM, Mel Gorman wrote:
> Page reclaim cleans individual pages using a_ops->writepage() because from
> the VM perspective, it is known that pages in a particular zone must be freed
> soon, it considers the target page to be the oldest and it does not want
> to wait while background flushers cleans other pages. From a filesystem
> perspective this is extremely inefficient as it generates a very seeky
> IO pattern leading to the perverse situation where it can take longer to
> clean all dirty pages than it would have otherwise.

Reclaiming clean pages should be fast enough that this should
make little, if any, difference.

> This patch queues all dirty pages at once to maximise the chances that
> the write requests get merged efficiently. It also makes the next patch
> that avoids writeout from direct reclaim more straight-forward.

However, this is a convincing argument :)

> Signed-off-by: Mel Gorman<mel@....ul.ie>

Reviewed-by: Rik van Riel <riel@...hat.com>

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