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

Matthew Wilcox
2022-02-14T18:08:36Z

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?