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

Pavel Begunkov
2025-02-26T02:05:57Z

On 2/26/25 01:53, Darrick J. Wong wrote:
> 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?

It can, if that's the preference, but iomap_dio_zero() would need
to have a separate check. It also affects 5.4, and I'm not sure
which version would be easier to back port.

--
Pavel Begunkov