Re: [PATCH v1 03/14] mm: add noio support in filemap_get_pages

Stefan Roesch
2022-02-16T18:27:26Z

On 2/14/22 10:08 AM, Matthew Wilcox wrote:
> On Mon, Feb 14, 2022 at 09:43:52AM -0800, Stefan Roesch wrote:
>> This adds noio support for async buffered writes in filemap_get_pages.
>> The idea is to handle the failure gracefully and return -EAGAIN if we
>> can't get the memory quickly.
>
> But it doesn't return -EAGAIN?
>
> folio = filemap_alloc_folio(mapping_gfp_mask(mapping), 0);
> if (!folio)
> return -ENOMEM;
>
>> Signed-off-by: Stefan Roesch <shr@fb.com>
>> ---
>> mm/filemap.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index d2fb817c0845..0ff4278c3961 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -2591,10 +2591,15 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter,
>> filemap_get_read_batch(mapping, index, last_index, fbatch);
>> }
>> if (!folio_batch_count(fbatch)) {
>> + unsigned int pflags;
>> +
>> if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
>> - return -EAGAIN;
>> + pflags = memalloc_noio_save();
>> err = filemap_create_folio(filp, mapping,
>> iocb->ki_pos >> PAGE_SHIFT, fbatch);
>> + if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ))
>> + memalloc_noio_restore(pflags);
>> +
>> if (err == AOP_TRUNCATED_PAGE)
>> goto retry;
>> return err;
>
> I would also not expect the memalloc_noio_save/restore calls to be
> here. Surely they should be at the top of the call chain where
> IOCB_NOWAIT/IOCB_WAITQ are set?

This patch will be removed from the next version of the patch series.