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Subject: Re: [PATCH] block: don't ignore REQ_NOWAIT for direct IO
From:   Pavel Begunkov <asml.silence@gmail.com>
To:     Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org
References: <546c66d26ae71abc151aa2074c3dd75ff5efb529.1605892141.git.asml.silence@gmail.com>
Cc:     linux-kernel@vger.kernel.org
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Message-ID: <19761b09-7c54-e9f2-681d-28e5bec66bc5@gmail.com>
Date:   Fri, 20 Nov 2020 17:13:19 +0000
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Precedence: bulk

On 20/11/2020 17:10, 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.

I'll leave it for judgement to those who know that code better,
but io_schedule() is gone from my traces.

> 
> 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);
>  
> @@ -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;
> 

-- 
Pavel Begunkov