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SubjectRe: [PATCH v4 3/3] fs: Add aio iopriority support for block_dev
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On 5/17/18 2:38 PM, adam.manzanares@wdc.com wrote:
> From: Adam Manzanares <adam.manzanares@wdc.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

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