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

Chenghao Duan
2026-03-23T11:08:12Z

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