Subject: [RFC PATCH v3 2/8] mm: compaction: handle non-lru compound pages properly in isolate_migratepages_block().

From: Zi Yan <[email-masked]>
Date: Wed, 5 Jan 2022 16:47:50 -0500

From: Zi Yan <[email-masked]>

In isolate_migratepages_block(), a !PageLRU tail page can be encountered
when the page is larger than a pageblock. Use compound head page for the
checks inside and skip the entire compound page when isolation succeeds.

Signed-off-by: Zi Yan <[email-masked]>
---
 mm/compaction.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index b4e94cda3019..ad9053fbbe06 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -979,19 +979,23 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		 * Skip any other type of page
 		 */
 		if (!PageLRU(page)) {
+			struct page *head = compound_head(page);
 			/*
 			 * __PageMovable can return false positive so we need
 			 * to verify it under page_lock.
 			 */
-			if (unlikely(__PageMovable(page)) &&
-					!PageIsolated(page)) {
+			if (unlikely(__PageMovable(head)) &&
+					!PageIsolated(head)) {
 				if (locked) {
 					unlock_page_lruvec_irqrestore(locked, flags);
 					locked = NULL;
 				}
 
-				if (!isolate_movable_page(page, isolate_mode))
+				if (!isolate_movable_page(head, isolate_mode)) {
+					low_pfn += (1 << compound_order(head)) - 1 - (page - head);
+					page = head;
 					goto isolate_success;
+				}
 			}
 
 			goto isolate_fail;
-- 
2.34.1