1 files changed, 31 insertions, 22 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index 74770e40cfe5..5039c964f5c8 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -367,22 +367,30 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 			goto isolate_fail;
 
 		/*
-		 * The zone lock must be held to isolate freepages.
-		 * Unfortunately this is a very coarse lock and can be
-		 * heavily contended if there are parallel allocations
-		 * or parallel compactions. For async compaction do not
-		 * spin on the lock and we acquire the lock as late as
-		 * possible.
+		 * If we already hold the lock, we can skip some rechecking.
+		 * Note that if we hold the lock now, checked_pageblock was
+		 * already set in some previous iteration (or strict is true),
+		 * so it is correct to skip the suitable migration target
+		 * recheck as well.
 		 */
-		if (!locked)
+		if (!locked) {
+			/*
+			 * The zone lock must be held to isolate freepages.
+			 * Unfortunately this is a very coarse lock and can be
+			 * heavily contended if there are parallel allocations
+			 * or parallel compactions. For async compaction do not
+			 * spin on the lock and we acquire the lock as late as
+			 * possible.
+			 */
 			locked = compact_trylock_irqsave(&cc->zone->lock,
 								&flags, cc);
-		if (!locked)
-			break;
+			if (!locked)
+				break;
 
-		/* Recheck this is a buddy page under lock */
-		if (!PageBuddy(page))
-			goto isolate_fail;
+			/* Recheck this is a buddy page under lock */
+			if (!PageBuddy(page))
+				goto isolate_fail;
+		}
 
 		/* Found a free page, break it into order-0 pages */
 		isolated = split_free_page(page);
@@ -644,19 +652,20 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		    page_count(page) > page_mapcount(page))
 			continue;
 
-		/* If the lock is not held, try to take it */
-		if (!locked)
+		/* If we already hold the lock, we can skip some rechecking */
+		if (!locked) {
 			locked = compact_trylock_irqsave(&zone->lru_lock,
 								&flags, cc);
-		if (!locked)
-			break;
+			if (!locked)
+				break;
 
-		/* Recheck PageLRU and PageTransHuge under lock */
-		if (!PageLRU(page))
-			continue;
-		if (PageTransHuge(page)) {
-			low_pfn += (1 << compound_order(page)) - 1;
-			continue;
+			/* Recheck PageLRU and PageTransHuge under lock */
+			if (!PageLRU(page))
+				continue;
+			if (PageTransHuge(page)) {
+				low_pfn += (1 << compound_order(page)) - 1;
+				continue;
+			}
 		}
 
 		lruvec = mem_cgroup_page_lruvec(page, zone);