Re: [PATCH 2/2] mm: support MIGRATE_DISCARD

[Michal Nazarewicz]

On Wed, Sep 05 2012, Minchan Kim wrote:
> This patch introudes MIGRATE_DISCARD mode in migration.
> It drops *clean cache pages* instead of migration so that
> migration latency could be reduced by avoiding (memcpy + page remapping).
> It's useful for CMA because latency of migration is very important rather
> than eviction of background processes's workingset. In addition, it needs
> less free pages for migration targets so it could avoid memory reclaiming
> to get free pages, which is another factor increase latency.
>
> Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>

The principle is very good (I always intended for CMA to discard clean
pages but simply did not have time to implement it), and the code looks
reasonably good to me.

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