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authorVlastimil Babka <vbabka@suse.cz>2014-10-09 15:27:07 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-10-09 22:25:54 -0400
commitf8224aa5a0a4627926019bba7511926393fbee3b (patch)
treeca92929dcf6b8d84382a9e2ccbe3ed2eb7800b25 /mm/compaction.c
parent98dd3b48a7b8e8277f14c2b7d879477efc1ed0d0 (diff)
mm, compaction: do not recheck suitable_migration_target under lock
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> Acked-by: 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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/compaction.c')
-rw-r--r--mm/compaction.c13
1 files changed, 0 insertions, 13 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index 1c7195d42e83..7bf150d4e1c8 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;