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SubjectRe: [PATCH] block: don't ignore REQ_NOWAIT for direct IO
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On 11/20/20 10:10 AM, Pavel Begunkov wrote:
> io_uring's direct nowait requests end up waiting on io_schedule() in
> sbitmap, that's seems to be so because blkdev_direct_IO() fails to
> propagate IOCB_NOWAIT to a bio and hence to blk-mq.
>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
> fs/block_dev.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 9e84b1928b94..e7e860c78d93 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -263,6 +263,8 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
> bio.bi_opf = dio_bio_write_op(iocb);
> task_io_account_write(ret);
> }
> + if (iocb->ki_flags & IOCB_NOWAIT)
> + bio.bi_opf |= REQ_NOWAIT;
> if (iocb->ki_flags & IOCB_HIPRI)
> bio_set_polled(&bio, iocb);

Was thinking this wasn't needed, but I guess that users could do sync && NOWAIT
and get -EAGAIN if using preadv2/pwritev2.

> @@ -416,6 +418,8 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
> bio->bi_opf = dio_bio_write_op(iocb);
> task_io_account_write(bio->bi_iter.bi_size);
> }
> + if (iocb->ki_flags & IOCB_NOWAIT)
> + bio->bi_opf |= REQ_NOWAIT;
>
> dio->size += bio->bi_iter.bi_size;
> pos += bio->bi_iter.bi_size;

Looks fine to me, we definitely should not be waiting on tags for IOCB_NOWAIT
IO. Will run some shakedown and test for 5.11.

--
Jens Axboe

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