mm: khugepaged: expand the is_refcount_suitable() to support file folios

Patch series "support shmem mTHP collapse", v2.

Shmem already supports mTHP allocation[1], and this patchset adds support
for shmem mTHP collapse, as well as adding relevant test cases.


This patch (of 5):

Expand the is_refcount_suitable() to support reference checks for file
folios, as preparation for supporting shmem mTHP collapse.

Link: https://lkml.kernel.org/r/cover.1724140601.git.baolin.wang@linux.alibaba.com
Link: https://lkml.kernel.org/r/eae4cb3195ebbb654bfb7967cb7261d4e4e7c7fa.1724140601.git.baolin.wang@linux.alibaba.comSigned-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Barry Song <21cnbao@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/khugepaged.c

@@ -546,12 +546,14 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
 
 static bool is_refcount_suitable(struct folio *folio)
 {
-	int expected_refcount;
+	int expected_refcount = folio_mapcount(folio);
 
-	expected_refcount = folio_mapcount(folio);
-	if (folio_test_swapcache(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;
 }
 
@@ -2285,8 +2287,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
 			break;
 		}
 
-		if (folio_ref_count(folio) !=
-		    1 + folio_mapcount(folio) + folio_test_private(folio)) {
+		if (!is_refcount_suitable(folio)) {
 			result = SCAN_PAGE_COUNT;
 			break;
 		}