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SubjectRe: [PATCH 6/6] mm: have order > 0 compaction start near a pageblock with free pages
On 08/07/2012 08:31 AM, Mel Gorman wrote:
> commit [7db8889a: mm: have order> 0 compaction start off where it left]
> introduced a caching mechanism to reduce the amount work the free page
> scanner does in compaction. However, it has a problem. Consider two process
> simultaneously scanning free pages
>
> C
> Process A M S F
> |---------------------------------------|
> Process B M FS

Argh. Good spotting.

> This is not optimal and it can still race but the compact_cached_free_pfn
> will be pointing to or very near a pageblock with free pages.

Agreed on the "not optimal", but I also cannot think of a better
idea right now. Getting this fixed for 3.6 is important, we can
think of future optimizations in San Diego.

> Signed-off-by: Mel Gorman<mgorman@suse.de>

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

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