Messages in this thread Patch in this message | | | From | Vlastimil Babka <> | Subject | [PATCH v3 03/13] mm, compaction: do not recheck suitable_migration_target under lock | Date | Fri, 20 Jun 2014 17:49:33 +0200 |
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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> --- mm/compaction.c | 13 ------------- 1 file changed, 13 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c index 7c491d0..3064a7f 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -276,7 +276,6 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, struct page *cursor, *valid_page = NULL; unsigned long flags; bool locked = false; - bool checked_pageblock = false; cursor = pfn_to_page(blockpfn); @@ -307,18 +306,6 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, if (!locked) break; - /* Recheck this is a suitable migration target under lock */ - if (!strict && !checked_pageblock) { - /* - * We need to check suitability of pageblock only once - * and this isolate_freepages_block() is called with - * pageblock range, so just check once is sufficient. - */ - checked_pageblock = true; - if (!suitable_migration_target(page)) - break; - } - /* Recheck this is a buddy page under lock */ if (!PageBuddy(page)) goto isolate_fail; -- 1.8.4.5
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