lkml.org 
[lkml]   [2014]   [Jul]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH V4 04/15] mm, compaction: do not recheck suitable_migration_target under lock
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


\
 
 \ /
  Last update: 2014-07-25 15:01    [W:0.153 / U:0.600 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site