Messages in this thread | | | Date | Fri, 25 Jul 2014 13:23:58 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH V4 04/15] mm, compaction: do not recheck suitable_migration_target under lock |
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On Wed, Jul 16, 2014 at 03:48:12PM +0200, Vlastimil Babka wrote: > isolate_freepages_block() rechecks if the pageblock is suitable to be a target > for migration after it has taken the zone->lock. However, the check has been > optimized to occur only once per pageblock, and compact_checklock_irqsave() > might be dropping and reacquiring lock, which means somebody else might have > changed the pageblock's migratetype meanwhile. > > Furthermore, nothing prevents the migratetype to change right after > isolate_freepages_block() has finished isolating. Given how imperfect this is, > it's simpler to just rely on the check done in isolate_freepages() without > lock, and not pretend that the recheck under lock guarantees anything. It is > just a heuristic after all. > > Signed-off-by: Vlastimil Babka <vbabka@suse.cz> > Reviewed-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com> > Acked-by: Minchan Kim <minchan@kernel.org> > Cc: Mel Gorman <mgorman@suse.de> > Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> > Cc: Michal Nazarewicz <mina86@mina86.com> > Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > Cc: Christoph Lameter <cl@linux.com> > Cc: Rik van Riel <riel@redhat.com> > Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Mel Gorman <mgorman@suse.de>
-- Mel Gorman SUSE Labs
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