Re: [PATCH 1/1] iomap: propagate nowait to block layer

Darrick J. Wong
2025-02-26T01:53:35Z

On Wed, Feb 26, 2025 at 01:33:58AM +0000, Pavel Begunkov wrote:
> There are reports of high io_uring submission latency for ext4 and xfs,
> which is due to iomap not propagating nowait flag to the block layer
> resulting in waiting for IO during tag allocation.
>
> Cc: stable@vger.kernel.org
> Link: https://github.com/axboe/liburing/issues/826#issuecomment-2674131870
> Reported-by: wu lei <uwydoc@gmail.com>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
> fs/iomap/direct-io.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index b521eb15759e..25c5e87dbd94 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -81,6 +81,9 @@ static void iomap_dio_submit_bio(const struct iomap_iter *iter,
> WRITE_ONCE(iocb->private, bio);
> }
>
> + if (iocb->ki_flags & IOCB_NOWAIT)
> + bio->bi_opf |= REQ_NOWAIT;

Shouldn't this go in iomap_dio_bio_opflags?

--D

> +
> if (dio->dops && dio->dops->submit_io)
> dio->dops->submit_io(iter, bio, pos);
> else
> --
> 2.48.1
>