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

On Thu, Mar 26 2026, Chenghao Duan wrote:

> 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>

Reviewed-by: Pratyush Yadav <pratyush@kernel.org>

BTW, can we also do the same for shmem_inode_acct_blocks() it the call
to it can also be aggregated in the same way? You don't have to do it in
this series, but possibly as a follow up.

[...]

-- 
Regards,
Pratyush Yadav