[PATCH 2/5] mm: khugepaged: use the number of pages in the folio to check the reference count

[Baolin Wang <baolin.wang@linux.alibaba.com>]

Use the number of pages in the folio to check the reference count as
preparation for supporting shmem mTHP collapse.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 mm/khugepaged.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index f11b4f172e61..60d95f08610c 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1994,7 +1994,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 		/*
 		 * We control three references to the folio:
 		 *  - we hold a pin on it;
-		 *  - one reference from page cache;
+		 *  - nr_pages reference from page cache;
 		 *  - one from lru_isolate_folio;
 		 * If those are the only references, then any new usage
 		 * of the folio will have to fetch it from the page
@@ -2002,7 +2002,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 		 * truncate, so any new usage will be blocked until we
 		 * unlock folio after collapse/during rollback.
 		 */
-		if (folio_ref_count(folio) != 3) {
+		if (folio_ref_count(folio) != 2 + folio_nr_pages(folio)) {
 			result = SCAN_PAGE_COUNT;
 			xas_unlock_irq(&xas);
 			folio_putback_lru(folio);
@@ -2185,7 +2185,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 		folio_clear_active(folio);
 		folio_clear_unevictable(folio);
 		folio_unlock(folio);
-		folio_put_refs(folio, 3);
+		folio_put_refs(folio, 2 + folio_nr_pages(folio));
 	}
 
 	goto out;
-- 
2.39.3