[PATCH v1 1/3] mm/memfd_luo: optimize shmem_recalc_inode calls in retrieve path

[Chenghao Duan]

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.

Signed-off-by: Chenghao Duan <duanchenghao@xxxxxxxxxx>
---
 mm/memfd_luo.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c
index b8edb9f981d7..5ddd3657d8be 100644
--- a/mm/memfd_luo.c
+++ b/mm/memfd_luo.c
@@ -397,6 +397,7 @@ static int memfd_luo_retrieve_folios(struct file *file,
 	struct folio *folio;
 	int err = -EIO;
 	long i;
+	u64 nr_added = 0;
 
 	for (i = 0; i < nr_folios; i++) {
 		const struct memfd_luo_folio_ser *pfolio = &folios_ser[i];
@@ -448,12 +449,15 @@ static int memfd_luo_retrieve_folios(struct file *file,
 			goto unlock_folio;
 		}
 
-		shmem_recalc_inode(inode, 1, 0);
+		nr_added++;
 		folio_add_lru(folio);
 		folio_unlock(folio);
 		folio_put(folio);
 	}
 
+	if (nr_added)
+		shmem_recalc_inode(inode, nr_added, 0);
+
 	return 0;
 
 unlock_folio:
@@ -472,6 +476,9 @@ static int memfd_luo_retrieve_folios(struct file *file,
 			folio_put(folio);
 	}
 
+	if (nr_added)
+		shmem_recalc_inode(inode, nr_added, 0);
+
 	return err;
 }
 
-- 
2.25.1