[PATCH 1/1] mm/migrate: correct nr_failed in migrate_pages_sync()

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

From: Zi Yan <ziy@nvidia.com>

nr_failed was missing the rc value from migrate_pages_batch() and can
cause a mismatch between migrate_pages() return value and the number of
not migrated pages, i.e., when the return value of migrate_pages() is 0,
there are still pages left in the from page list. It will happen when a
non-PMD THP large folio fails to migrate due to -ENOMEM and is split
successfully but not all the split pages are not migrated,
migrate_pages_batch() would return non-zero, but astats.nr_thp_split = 0.
nr_failed would be 0 and returned to the caller of migrate_pages(), but
the not migrated pages are left in the from page list without being added
back to LRU lists.

Fixes: 2ef7dbb26990 ("migrate_pages: try migrate in batch asynchronously firstly")
Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/migrate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index c602bf6dec97..5348827bd958 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1834,7 +1834,7 @@ static int migrate_pages_sync(struct list_head *from, new_folio_t get_new_folio,
 		return rc;
 	}
 	stats->nr_thp_failed += astats.nr_thp_split;
-	nr_failed += astats.nr_thp_split;
+	nr_failed += rc + astats.nr_thp_split;
 	/*
 	 * Fall back to migrate all failed folios one by one synchronously. All
 	 * failed folios except split THPs will be retried, so their failure
-- 
2.42.0