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

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Date:	Thu, 13 Mar 2014 15:05:12 +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 Thu, Mar 13, 2014 at 03:37:46PM +0100, Bartlomiej Zolnierkiewicz wrote:
> On Thursday, March 13, 2014 02:25:40 PM Mel Gorman wrote:
> > 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>
> 
> Thanks but does that mean that v3 should be abandoned:
> 
> 	https://lkml.org/lkml/2014/3/6/365
> 

Bah, no. v3 looks better. I was going through the vast pile of mail marked
unread and thought it must be the latest version if it was still "new"
and didn't search linux-mm. I was obviously thinking more clearly when I
saw v2 the first time.

Sorry for the confusion.

-- 
Mel Gorman
SUSE Labs
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