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. Suggested-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> Signed-off-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx> --- 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); -- 1.8.3.1
