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

[Pratyush Yadav <pratyush@kernel.org>]

On Thu, Mar 19 2026, Pasha Tatashin wrote:

> On Wed, Mar 18, 2026 at 9:29 PM Chenghao Duan <duanchenghao@kylinos.cn> 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@kylinos.cn>
>> ---
>>  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.

It is though, for the most part. I also prefer this so as much as I
could I followed it, but sometimes if you want to assign variables at
declaration, it isn't always possible.

Anyway, RCT would be nice to have indeed.

[...]

-- 
Regards,
Pratyush Yadav