Re: [patch v2 2/4] mm, compaction: return failed migration target pages back to freelist

[Mel Gorman]

On Thu, May 01, 2014 at 02:35:42PM -0700, David Rientjes wrote:
> Memory compaction works by having a "freeing scanner" scan from one end of a 
> zone which isolates pages as migration targets while another "migrating scanner" 
> scans from the other end of the same zone which isolates pages for migration.
> 
> When page migration fails for an isolated page, the target page is returned to 
> the system rather than the freelist built by the freeing scanner.  This may 
> require the freeing scanner to continue scanning memory after suitable migration 
> targets have already been returned to the system needlessly.
> 
> This patch returns destination pages to the freeing scanner freelist when page 
> migration fails.  This prevents unnecessary work done by the freeing scanner but 
> also encourages memory to be as compacted as possible at the end of the zone.
> 
> Reported-by: Greg Thelen <gthelen@xxxxxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxx>

-- 
Mel Gorman
SUSE Labs
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