[PATCH v2 2/4] mm/memfd_luo: optimize shmem_recalc_inode calls in retrieve path

Chenghao Duan
2026-03-23T11:08:07Z

Move shmem_recalc_inode() out of the loop in memfd_luo_retrieve_folios()
to improve performance when restoring large memfds.

Currently, shmem_recalc_inode() is called for each folio during restore,
which is O(n) expensive operations. This patch collects the number of
successfully added folios and calls shmem_recalc_inode() once after the
loop completes, reducing complexity to O(1).

Additionally, fix the error path to also call shmem_recalc_inode() for
the folios that were successfully added before the error occurred.

Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
---
mm/memfd_luo.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c
index 953440994ad2..2a01eaff03c2 100644
--- a/mm/memfd_luo.c
+++ b/mm/memfd_luo.c
@@ -395,7 +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;
+ long npages, nr_added_pages = 0;
int err = -EIO;
long i;

@@ -450,12 +450,14 @@ static int memfd_luo_retrieve_folios(struct file *file,
goto unlock_folio;
}

- shmem_recalc_inode(inode, npages, 0);
+ nr_added_pages += npages;
folio_add_lru(folio);
folio_unlock(folio);
folio_put(folio);
}

+ shmem_recalc_inode(inode, nr_added_pages, 0);
+
return 0;

unlock_folio:
@@ -474,6 +476,8 @@ static int memfd_luo_retrieve_folios(struct file *file,
folio_put(folio);
}

+ shmem_recalc_inode(inode, nr_added_pages, 0);
+
return err;
}

--
2.25.1