Re: [PATCH 5/7] mm: vmscan: Do not writeback filesystem pages inkswapd except in high priority

From: Rik van Riel
Date: Thu Aug 11 2011 - 14:19:30 EST

On 08/10/2011 06:47 AM, Mel Gorman 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@xxxxxxx>
Reviewed-by: Minchan Kim<>

My only worry with this patch is that maybe we'll burn too
much CPU time freeing pages from a zone. However, chances
are we'll have freed pages from other zones when scanning
one zone multiple times (the page cache dirty limit is global,
the clean pages have to be _somewhere_).

Since the bulk of the allocators are not too picky about
which zone they get their pages from, I suspect this patch
will be an overall improvement pretty much all the time.

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