[PATCH v1 11/18] mm/migrate: use folio_likely_mapped_shared() in add_page_for_migration()

We want to limit the use of page_mapcount() to the places where it is
absolutely necessary. In add_page_for_migration(), we actually want to
check if the folio is mapped shared, to reject such folios. So let's
use folio_likely_mapped_shared() instead.

For small folios, fully mapped THP, and hugetlb folios, there is no change.
For partially mapped, shared THP, we should now do a better job at
rejecting such folios.

Signed-off-by: David Hildenbrand <[email protected]>
---
 mm/migrate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 285072bca29c..d87ce32645d4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2140,7 +2140,7 @@ static int add_page_for_migration(struct mm_struct *mm, const void __user *p,
 		goto out_putfolio;
 
 	err = -EACCES;
-	if (page_mapcount(page) > 1 && !migrate_all)
+	if (folio_likely_mapped_shared(folio) && !migrate_all)
 		goto out_putfolio;
 
 	err = -EBUSY;
-- 
2.44.0