linux-kernel - Re: [PATCH v4 3/3] fs: Add aio iopriority support for block

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Date:   Fri, 18 May 2018 09:14:07 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     adam.manzanares@....com, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org, bcrl@...ck.org
Cc:     mingo@...nel.org, peterz@...radead.org, pombredanne@...b.com,
        gregkh@...uxfoundation.org, bigeasy@...utronix.de,
        rgoldwyn@...e.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-aio@...ck.org,
        linux-api@...r.kernel.org
Subject: Re: [PATCH v4 3/3] fs: Add aio iopriority support for block_dev

On 5/17/18 2:38 PM, adam.manzanares@....com wrote:
> From: Adam Manzanares <adam.manzanares@....com>
> 
> This is the per-I/O equivalent of the ioprio_set system call.
> 
> When IOCB_FLAG_IOPRIO is set on the iocb aio_flags field, then we set the
> newly added kiocb ki_ioprio field to the value in the iocb aio_reqprio field.
> 
> When a bio is created for an aio request by the block dev we set the priority
> value of the bio to the user supplied value.
> 
> This patch depends on block: add ioprio_check_cap function

Actually, one comment on this one:

> diff --git a/fs/aio.c b/fs/aio.c
> index f3eae5d5771b..ff3107aa82d5 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1451,6 +1451,22 @@ static int aio_prep_rw(struct kiocb *req, struct iocb *iocb)
>  	if (iocb->aio_flags & IOCB_FLAG_RESFD)
>  		req->ki_flags |= IOCB_EVENTFD;
>  	req->ki_hint = file_write_hint(req->ki_filp);
> +	if (iocb->aio_flags & IOCB_FLAG_IOPRIO) {
> +		/*
> +		 * If the IOCB_FLAG_IOPRIO flag of aio_flags is set, then
> +		 * aio_reqprio is interpreted as an I/O scheduling
> +		 * class and priority.
> +		 */
> +		ret = ioprio_check_cap(iocb->aio_reqprio);
> +		if (ret) {
> +			pr_debug("aio ioprio check cap error\n");
> +			return -EINVAL;
> +		}
> +
> +		req->ki_ioprio = iocb->aio_reqprio;
> +		req->ki_flags |= IOCB_IOPRIO;
> +	}

Do we really need IOCB_IOPRIO? All zeroes is no priority set anyway,
so we should be able to get by with just setting ->ki_ioprio to either
the priority, or 0.

> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 7ec920e27065..970bef79caa6 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -355,6 +355,8 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>  		bio->bi_write_hint = iocb->ki_hint;
>  		bio->bi_private = dio;
>  		bio->bi_end_io = blkdev_bio_end_io;
> +		if (iocb->ki_flags & IOCB_IOPRIO)
> +			bio->bi_ioprio = iocb->ki_ioprio;

And then this assignment can just happen unconditionally.

-- 
Jens Axboe