Re: [PATCH v3 4/4] io_uring: add support for zone-append

Jens Axboe
2020-07-05T21:00:51Z

On 7/5/20 12:47 PM, Kanchan Joshi wrote:
> From: Selvakumar S <selvakuma.s1@samsung.com>
>
> For zone-append, block-layer will return zone-relative offset via ret2
> of ki_complete interface. Make changes to collect it, and send to
> user-space using cqe->flags.
>
> Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
> ---
> fs/io_uring.c | 21 +++++++++++++++++++--
> 1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 155f3d8..cbde4df 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -402,6 +402,8 @@ struct io_rw {
> struct kiocb kiocb;
> u64 addr;
> u64 len;
> + /* zone-relative offset for append, in sectors */
> + u32 append_offset;
> };

I don't like this very much at all. As it stands, the first cacheline
of io_kiocb is set aside for request-private data. io_rw is already
exactly 64 bytes, which means that you're now growing io_rw beyond
a cacheline and increasing the size of io_kiocb as a whole.

Maybe you can reuse io_rw->len for this, as that is only used on the
submission side of things.

--
Jens Axboe