On Wed, 10 Aug 2011 11:47:18 +0100
Mel Gorman [off-list ref] wrote:

It is preferable that no dirty pages are dispatched for cleaning from
the page reclaim path. At normal priorities, this patch prevents kswapd
writing pages.

However, page reclaim does have a requirement that pages be freed
in a particular zone. If it is failing to make sufficient progress
(reclaiming < SWAP_CLUSTER_MAX at any priority priority), the priority
is raised to scan more pages. A priority of DEF_PRIORITY - 3 is
considered to be the point where kswapd is getting into trouble
reclaiming pages. If this priority is reached, kswapd will dispatch
pages for writing.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Minchan Kim <redacted>

Reviewed-by: KAMEZAWA Hiroyuki <redacted>

BTW, I'd like to see summary of the effect of priority..

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