mm/khugepaged: clean up refcount check using folio_expected_ref_count()

Use folio_expected_ref_count() instead of open-coded logic in
is_refcount_suitable().  This avoids code duplication and improves
clarity.

Drop is_refcount_suitable() as it is no longer needed.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Shivank Garg <[email protected]>
Suggested-by: David Hildenbrand <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Acked-by: Dev Jain <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Cc: Bharata B Rao <[email protected]>
Cc: Fengwei Yin <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Mariano Pache <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: shivankgarg98

mm/khugepaged.c

@@ -548,19 +548,6 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
 	}
 }
 
-static bool is_refcount_suitable(struct folio *folio)
-{
-	int expected_refcount = folio_mapcount(folio);
-
-	if (!folio_test_anon(folio) || folio_test_swapcache(folio))
-		expected_refcount += folio_nr_pages(folio);
-
-	if (folio_test_private(folio))
-		expected_refcount++;
-
-	return folio_ref_count(folio) == expected_refcount;
-}
-
 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 					unsigned long address,
 					pte_t *pte,
@@ -652,7 +639,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 		 * but not from this process. The other process cannot write to
 		 * the page, only trigger CoW.
 		 */
-		if (!is_refcount_suitable(folio)) {
+		if (folio_expected_ref_count(folio) != folio_ref_count(folio)) {
 			folio_unlock(folio);
 			result = SCAN_PAGE_COUNT;
 			goto out;
@@ -1402,7 +1389,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
 		 * has excessive GUP pins (i.e. 512).  Anyway the same check
 		 * will be done again later the risk seems low.
 		 */
-		if (!is_refcount_suitable(folio)) {
+		if (folio_expected_ref_count(folio) != folio_ref_count(folio)) {
 			result = SCAN_PAGE_COUNT;
 			goto out_unmap;
 		}