Re: [PATCH] block: don't ignore REQ_NOWAIT for direct IO

From: Pavel Begunkov
Date: Fri Apr 02 2021 - 10:28:20 EST


On 20/11/2020 19:13, Jens Axboe wrote:
> 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@xxxxxxxxx>
>> ---
>> 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.
>

up

--
Pavel Begunkov