linux-kernel - Re: [RFC][PATCH v2] mm/page_alloc: fix freeing of MIGRATE

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Date:	Thu, 13 Mar 2014 14:25:40 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Yong-Taek Lee <ytk.lee@...sung.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH v2] mm/page_alloc: fix freeing of MIGRATE_RESERVE
 migratetype pages

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@...sung.com>
> Reported-by: Yong-Taek Lee <ytk.lee@...sung.com>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Hugh Dickins <hughd@...gle.com>

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@...e.de>

-- 
Mel Gorman
SUSE Labs
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