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

[Pasha Tatashin]

On Wed, Mar 18, 2026 at 9:29 PM Chenghao Duan <duanchenghao@xxxxxxxxxx> 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.
>
> 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;

nit: I perfer RCT for local variables order, but it is not followed in
this file anyway.

>
>         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);
> +

Reviewed-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>