Re: [PATCH v3 RESEND] iomap: set REQ_NOWAIT according to IOCB_NOWAIT in Direct IO

[Pavel Begunkov <asml.silence@gmail.com>]

On 04/12/2020 09:44, Hao Xu wrote:
> Currently, IOCB_NOWAIT is ignored in Direct IO, REQ_NOWAIT is only set
> when IOCB_HIPRI is set. But REQ_NOWAIT should be set as well when
> IOCB_NOWAIT is set.

I believe Jens took my patch fixing that for blkdev_direct_IO*()
(but not iomap) a while ago.

BTW, even though get_maintainer.pl doesn't think so, AFAIK
fs/block_dev.c is managed by linux-block@vger.kernel.org. Please CC it
next time.

> Suggested-by: Jeffle Xu <jefflexu@linux.alibaba.com>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
> ---
> 
> Hi all,
> I tested fio io_uring direct read for a file on ext4 filesystem on a
> nvme ssd. I found that IOCB_NOWAIT is ignored in iomap layer, which
> means REQ_NOWAIT is not set in bio->bi_opf. This makes nowait IO a
> normal IO. Since I'm new to iomap and block layer, I sincerely ask
> yours opinions in case I misunderstand the code which is very likely
> to happen.:)
> The example I use: io_uring direct randread, the first try is with
> IOCB_NOWAIT but not IOCB_HIPRI, the IOCB_NOWAIT is ignored in block
> layer which I think is not the designed behaviour.
> 
> I found that Konstantin found this issue before in May
> 2020 (https://www.spinics.net/lists/linux-block/msg53275.html), here add
> his signature, add Jeffle's as well since he gave me some help.
> 
> v1->v2:
> * add same logic in __blkdev_direct_IO_simple()
> v2->v3:
> * add same logic in do_blockdev_direct_IO()
> 
>  fs/block_dev.c       | 7 +++++++
>  fs/direct-io.c       | 6 ++++--
>  fs/iomap/direct-io.c | 3 +++
>  3 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 9e84b1928b94..ca6f365c2f14 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -263,6 +263,10 @@ static void blkdev_bio_end_io_simple(struct bio *bio)
>  		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);
>  
> @@ -417,6 +421,9 @@ static void blkdev_bio_end_io(struct bio *bio)
>  			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;
>  
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index d53fa92a1ab6..b221ed351c1c 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -1206,11 +1206,13 @@ static inline int drop_refcount(struct dio *dio)
>  	if (iov_iter_rw(iter) == WRITE) {
>  		dio->op = REQ_OP_WRITE;
>  		dio->op_flags = REQ_SYNC | REQ_IDLE;
> -		if (iocb->ki_flags & IOCB_NOWAIT)
> -			dio->op_flags |= REQ_NOWAIT;
>  	} else {
>  		dio->op = REQ_OP_READ;
>  	}
> +
> +	if (iocb->ki_flags & IOCB_NOWAIT)
> +		dio->op_flags |= REQ_NOWAIT;
> +
>  	if (iocb->ki_flags & IOCB_HIPRI)
>  		dio->op_flags |= REQ_HIPRI;
>  
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 933f234d5bec..2e897688ed6d 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -64,6 +64,9 @@ static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
>  {
>  	atomic_inc(&dio->ref);
>  
> +	if (dio->iocb->ki_flags & IOCB_NOWAIT)
> +		bio->bi_opf |= REQ_NOWAIT;
> +
>  	if (dio->iocb->ki_flags & IOCB_HIPRI)
>  		bio_set_polled(bio, dio->iocb);
>  
> 

-- 
Pavel Begunkov