[PATCH] mm/migrate: make migrate_pages_batch() stats consistent.

[Zi Yan <zi.yan@sent.com>]

From: Zi Yan <ziy@nvidia.com>

As Ying pointed out in [1], stats->nr_thp_failed needs to be updated to
avoid stats inconsistency between MIGRATE_SYNC and MIGRATE_ASYNC when
calling migrate_pages_batch().

[1] https://lore.kernel.org/linux-mm/87msnq7key.fsf@yhuang6-desk2.ccr.corp.intel.com/

Suggested-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/migrate.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index 2cc5a68f6843..20cb9f5f7446 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1659,6 +1659,10 @@ static int migrate_pages_batch(struct list_head *from,
 			 * migrate_pages() may report success with (split but
 			 * unmigrated) pages still on its fromlist; whereas it
 			 * always reports success when its fromlist is empty.
+			 * stats->nr_thp_failed should be increased too,
+			 * otherwise stats inconsistency will happen when
+			 * migrate_pages_batch is called via migrate_pages()
+			 * with MIGRATE_SYNC and MIGRATE_ASYNC.
 			 *
 			 * Only check it without removing it from the list.
 			 * Since the folio can be on deferred_split_scan()
@@ -1675,6 +1679,7 @@ static int migrate_pages_batch(struct list_head *from,
 			   !list_empty(&folio->_deferred_list)) {
 				if (try_split_folio(folio, split_folios) == 0) {
 					nr_failed++;
+					stats->nr_thp_failed += is_thp;
 					stats->nr_thp_split += is_thp;
 					stats->nr_split++;
 					continue;

base-commit: 14d7c92f8df9c0964ae6f8b813c1b3ac38120825
-- 
2.43.0