Re: [RFC][PATCH v2] mm/page_alloc: fix freeing of MIGRATE_RESERVE migratetype pages

[Mel Gorman]

On Fri, Feb 14, 2014 at 07:34:17PM +0100, Bartlomiej Zolnierkiewicz wrote:
> Pages allocated from MIGRATE_RESERVE migratetype pageblocks
> are not freed back to MIGRATE_RESERVE migratetype free
> lists in free_pcppages_bulk()->__free_one_page() if we got
> to free_pcppages_bulk() through drain_[zone_]pages().
> The freeing through free_hot_cold_page() is okay because
> freepage migratetype is set to pageblock migratetype before
> calling free_pcppages_bulk().  If pages of MIGRATE_RESERVE
> migratetype end up on the free lists of other migratetype
> whole Reserved pageblock may be later changed to the other
> migratetype in __rmqueue_fallback() and it will be never
> changed back to be a Reserved pageblock.  Fix the issue by
> preserving freepage migratetype as a pageblock migratetype
> (instead of overriding it to the requested migratetype)
> for MIGRATE_RESERVE migratetype pages in rmqueue_bulk().
> 
> The problem was introduced in v2.6.31 by commit ed0ae21
> ("page allocator: do not call get_pageblock_migratetype()
> more than necessary").
> 
> Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
> Reported-by: Yong-Taek Lee <ytk.lee@xxxxxxxxxxx>
> Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>

It's a pity about the unconditional pageblock lookup in that path but I
didn't see a better way around it so

Acked-by: Mel Gorman <mgorman@xxxxxxx>

-- 
Mel Gorman
SUSE Labs
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