Re: [PATCH v2 2/3] block: io_uring: add READV_PI/WRITEV_PI operations

[Jens Axboe <axboe@kernel.dk>]

On 2/10/22 6:08 AM, Alexander V. Buev wrote:
> Added new READV_PI/WRITEV_PI operations to io_uring.
> Added new pi_addr & pi_len fields to SQE struct.
> Added new pi_iter field and IOCB_USE_PI flag to kiocb struct.
> Make corresponding corrections to io uring trace event.
> 
> Signed-off-by: Alexander V. Buev <a.buev@yadro.com>
> ---
>  fs/io_uring.c                   | 209 ++++++++++++++++++++++++++++++++
>  include/linux/fs.h              |   2 +
>  include/trace/events/io_uring.h |  17 +--
>  include/uapi/linux/io_uring.h   |   6 +-
>  include/uapi/linux/uio.h        |   3 +-
>  5 files changed, 228 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 2e04f718319d..6e941040f228 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -563,6 +563,19 @@ struct io_rw {
>  	u64				len;
>  };
>  
> +struct io_rw_pi_state {
> +	struct iov_iter			iter;
> +	struct iov_iter_state		iter_state;
> +	struct iovec			fast_iov[UIO_FASTIOV_PI];
> +};
> +
> +struct io_rw_pi {
> +	struct io_rw			rw;
> +	struct iovec			*pi_iov;
> +	u32				nr_pi_segs;
> +	struct io_rw_pi_state		*s;
> +};

One immediate issue I see here is that io_rw_pi is big, and we try very
hard to keep the per-command payload to 64-bytes. This would be 88 bytes
by my count :-/

Do you need everything from io_rw? If not, I'd just make io_rw_pi
contain the bits you need and see if you can squeeze it into the
existing cacheline.

-- 
Jens Axboe