mm-compaction-acquire-the-zone-lru_lock-as-late-as-possible-fix

augment comment

Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/compaction.c b/mm/compaction.c
index a0c1a08c4172ab221d8c74d7292bc0042059ec62..7d96f8b45aa8fe75fe4751be12b85f8d6c384227 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -415,7 +415,8 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
                 * if PageLRU is set) but the lock is not necessarily taken
                 * here and it is wasteful to take it just to check transhuge.
                 * Check transhuge without lock and skip if it's either a
-                * transhuge or hugetlbfs page.
+                * transhuge or hugetlbfs page because calling compound_order()
+                * requires lru_lock to exclude isolation and splitting.
                 */
                if (PageTransHuge(page)) {
                        if (!locked)