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

From: Rik van Riel
Date: Mon Jun 14 2010 - 17:14:36 EST

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@xxxxxxxxx>

Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>

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