From: Michal Hocko <mhocko@suse.cz>
To: Mel Gorman <mgorman@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Minchan Kim <minchan.kim@gmail.com>,
Thomas Sattler <tsattler@gmx.de>,
Ury Stankevich <urykhy@gmail.com>,
Andi Kleen <andi@firstfloor.org>, linux-mm <linux-mm@kvack.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/4] mm: compaction: Ensure that the compaction free scanner does not move to the next zone
Date: Wed, 8 Jun 2011 11:33:10 +0200 [thread overview]
Message-ID: <20110608093310.GC6742@tiehlicka.suse.cz> (raw)
In-Reply-To: <1307459225-4481-2-git-send-email-mgorman@suse.de>
On Tue 07-06-11 16:07:02, Mel Gorman wrote:
> Compaction works with two scanners, a migration and a free
> scanner. When the scanners crossover, migration within the zone is
> complete. The location of the scanner is recorded on each cycle to
> avoid excesive scanning.
>
> When a zone is small and mostly reserved, it's very easy for the
> migration scanner to be close to the end of the zone. Then the following
> situation can occurs
>
> o migration scanner isolates some pages near the end of the zone
> o free scanner starts at the end of the zone but finds that the
> migration scanner is already there
> o free scanner gets reinitialised for the next cycle as
> cc->migrate_pfn + pageblock_nr_pages
> moving the free scanner into the next zone
> o migration scanner moves into the next zone
>
> When this happens, NR_ISOLATED accounting goes haywire because some
> of the accounting happens against the wrong zone. One zones counter
> remains positive while the other goes negative even though the overall
> global count is accurate. This was reported on X86-32 with !SMP because
> !SMP allows the negative counters to be visible. The fact that it is
> difficult to reproduce on X86-64 is probably just a co-incidence as
> the bug should theoritically be possible there.
>
> Signed-off-by: Mel Gorman <mgorman@suse.de>
> Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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next prev parent reply other threads:[~2011-06-08 9:33 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-07 15:07 [PATCH 0/4] Fix compaction stalls due to accounting errors in isolated page accounting Mel Gorman
2011-06-07 15:07 ` [PATCH 1/4] mm: compaction: Ensure that the compaction free scanner does not move to the next zone Mel Gorman
2011-06-08 9:33 ` Michal Hocko [this message]
2011-06-07 15:07 ` [PATCH 2/4] mm: vmscan: Do not use page_count without a page pin Mel Gorman
2011-06-07 15:12 ` Minchan Kim
2011-06-08 9:38 ` Michal Hocko
2011-06-07 15:07 ` [PATCH 3/4] mm: memory-failure: Fix isolated page count during memory failure Mel Gorman
2011-06-07 15:14 ` Minchan Kim
2011-06-08 10:07 ` Michal Hocko
2011-06-08 10:11 ` Michal Hocko
2011-06-07 15:07 ` [PATCH 4/4] mm: compaction: Abort compaction if too many pages are isolated and caller is asynchronous Mel Gorman
2011-06-07 15:50 ` Minchan Kim
2011-06-07 16:26 ` Mel Gorman
2011-06-07 16:27 ` [PATCH 4/4] mm: compaction: Abort compaction if too many pages are isolated and caller is asynchronous V2 Mel Gorman
2011-06-07 16:36 ` Minchan Kim
2011-06-08 9:55 ` Michal Hocko
2011-07-17 8:52 ` [PATCH 0/4] Fix compaction stalls due to accounting errors in isolated page accounting Thomas Sattler
2011-07-19 9:16 ` Mel Gorman
2011-07-19 11:24 ` Thomas Sattler
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