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);