1 files changed, 27 insertions, 20 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index 0dce7e87d771..1ccb015ab1eb 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -680,6 +680,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 
 	/* Time to isolate some pages for migration */
 	for (; low_pfn < end_pfn; low_pfn++) {
+		bool is_lru;
+
 		/*
 		 * Periodically drop the lock (if held) regardless of its
 		 * contention, to give chance to IRQs. Abort async compaction
@@ -723,36 +725,35 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		 * It's possible to migrate LRU pages and balloon pages
 		 * Skip any other type of page
 		 */
-		if (!PageLRU(page)) {
+		is_lru = PageLRU(page);
+		if (!is_lru) {
 			if (unlikely(balloon_page_movable(page))) {
 				if (balloon_page_isolate(page)) {
 					/* Successfully isolated */
 					goto isolate_success;
 				}
 			}
-			continue;
 		}
 
 		/*
-		 * PageLRU is set. lru_lock normally excludes isolation
-		 * splitting and collapsing (collapsing has already happened
-		 * 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 the whole pageblock if
-		 * it's either a transhuge or hugetlbfs page, as calling
-		 * compound_order() without preventing THP from splitting the
-		 * page underneath us may return surprising results.
+		 * Regardless of being on LRU, compound pages such as THP and
+		 * hugetlbfs are not to be compacted. We can potentially save
+		 * a lot of iterations if we skip them at once. The check is
+		 * racy, but we can consider only valid values and the only
+		 * danger is skipping too much.
 		 */
-		if (PageTransHuge(page)) {
-			if (!locked)
-				low_pfn = ALIGN(low_pfn + 1,
-						pageblock_nr_pages) - 1;
-			else
-				low_pfn += (1 << compound_order(page)) - 1;
+		if (PageCompound(page)) {
+			unsigned int comp_order = compound_order(page);
+
+			if (likely(comp_order < MAX_ORDER))
+				low_pfn += (1UL << comp_order) - 1;
 
 			continue;
 		}
 
+		if (!is_lru)
+			continue;
+
 		/*
 		 * Migration will fail if an anonymous page is pinned in memory,
 		 * so avoid taking lru_lock and isolating it unnecessarily in an
@@ -769,11 +770,17 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 			if (!locked)
 				break;
 
-			/* Recheck PageLRU and PageTransHuge under lock */
+			/* Recheck PageLRU and PageCompound under lock */
 			if (!PageLRU(page))
 				continue;
-			if (PageTransHuge(page)) {
-				low_pfn += (1 << compound_order(page)) - 1;
+
+			/*
+			 * Page become compound since the non-locked check,
+			 * and it's on LRU. It can only be a THP so the order
+			 * is safe to read and it's 0 for tail pages.
+			 */
+			if (unlikely(PageCompound(page))) {
+				low_pfn += (1UL << compound_order(page)) - 1;
 				continue;
 			}
 		}
@@ -784,7 +791,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		if (__isolate_lru_page(page, isolate_mode) != 0)
 			continue;
 
-		VM_BUG_ON_PAGE(PageTransCompound(page), page);
+		VM_BUG_ON_PAGE(PageCompound(page), page);
 
 		/* Successfully isolated */
 		del_page_from_lru_list(page, lruvec, page_lru(page));