[PATCH v2 1/4] mm/memfd: use folio_nr_pages() for shmem inode accounting

[Chenghao Duan <duanchenghao@kylinos.cn>]

memfd_luo_retrieve_folios() called shmem_inode_acct_blocks() and
shmem_recalc_inode() with hardcoded 1 instead of the actual folio
page count.  memfd may use large folios (THP/hugepages), causing
quota/limit under-accounting and incorrect stat output.

Fix by using folio_nr_pages(folio) for both functions.

Issue found by AI review and suggested by Pratyush Yadav <pratyush@kernel.org>.
https://sashiko.dev/#/patchset/20260319012845.29570-1-duanchenghao%40kylinos.cn

Suggested-by: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
---
 mm/memfd_luo.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c
index b8edb9f981d7..953440994ad2 100644
--- a/mm/memfd_luo.c
+++ b/mm/memfd_luo.c
@@ -395,6 +395,7 @@ static int memfd_luo_retrieve_folios(struct file *file,
 	struct inode *inode = file_inode(file);
 	struct address_space *mapping = inode->i_mapping;
 	struct folio *folio;
+	long npages;
 	int err = -EIO;
 	long i;
 
@@ -441,14 +442,15 @@ static int memfd_luo_retrieve_folios(struct file *file,
 		if (flags & MEMFD_LUO_FOLIO_DIRTY)
 			folio_mark_dirty(folio);
 
-		err = shmem_inode_acct_blocks(inode, 1);
+		npages = folio_nr_pages(folio);
+		err = shmem_inode_acct_blocks(inode, npages);
 		if (err) {
-			pr_err("shmem: failed to account folio index %ld: %d\n",
-			       i, err);
+			pr_err("shmem: failed to account folio index %ld(%ld pages): %d\n",
+			       i, npages, err);
 			goto unlock_folio;
 		}
 
-		shmem_recalc_inode(inode, 1, 0);
+		shmem_recalc_inode(inode, npages, 0);
 		folio_add_lru(folio);
 		folio_unlock(folio);
 		folio_put(folio);
-- 
2.25.1