Re: [PATCH 6/6] mm: have order > 0 compaction start near a pageblockwith free pages

[Rik van Riel]

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@xxxxxxx>

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

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