Re: [PATCH] mm: cma: Discard clean pages during contiguousallocation instead of migration

From: Mel Gorman
Date: Tue Sep 11 2012 - 05:00:02 EST

On Tue, Sep 11, 2012 at 09:41:52AM +0900, Minchan Kim wrote:
> This patch drops clean cache pages instead of migration during
> alloc_contig_range() to minimise allocation latency by reducing the amount
> of migration is necessary. It's useful for CMA because latency of migration
> is more important than evicting the background processes working set.
> In addition, as pages are reclaimed then fewer free pages for migration
> targets are required so it avoids memory reclaiming to get free pages,
> which is a contributory factor to increased latency.
> * from v1
> * drop migrate_mode_t
> * add reclaim_clean_pages_from_list instad of MIGRATE_DISCARD support - Mel
> I measured elapsed time of __alloc_contig_migrate_range which migrates
> 10M in 40M movable zone in QEMU machine.
> Before - 146ms, After - 7ms
> Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>

My signed-off is already on this but in earlier versions I was still
asking for changes. This time the patch looks good to me so even though
it is a bit redundant.

Reviewed-by: Mel Gorman <mgorman@xxxxxxx>

Thanks Minchan.

Mel Gorman
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