Re: [PATCH 06/12] scsi: iscsi_tcp: Use sendpage for the PDU header

[Lee Duncan <lduncan@suse.com>]

On 3/7/22 16:27, Mike Christie wrote:
> This has us use zero copy the PDU header.
> 
> Signed-off-by: Mike Christie <michael.christie@oracle.com>
> ---
>   drivers/scsi/iscsi_tcp.c | 30 ++++++++++++++++++++++--------
>   1 file changed, 22 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/scsi/iscsi_tcp.c b/drivers/scsi/iscsi_tcp.c
> index 261599938fc9..3bdefc4b6b17 100644
> --- a/drivers/scsi/iscsi_tcp.c
> +++ b/drivers/scsi/iscsi_tcp.c
> @@ -306,7 +306,7 @@ static int iscsi_sw_tcp_xmit_segment(struct iscsi_tcp_conn *tcp_conn,
>   		copy = segment->size - offset;
>   
>   		if (segment->total_copied + segment->size < segment->total_size)
> -			flags |= MSG_MORE;
> +			flags |= MSG_MORE | MSG_SENDPAGE_NOTLAST;
>   
>   		/* Use sendpage if we can; else fall back to sendmsg */
>   		if (!segment->data) {
> @@ -315,13 +315,27 @@ static int iscsi_sw_tcp_xmit_segment(struct iscsi_tcp_conn *tcp_conn,
>   			r = tcp_sw_conn->sendpage(sk, sg_page(sg), offset,
>   						  copy, flags);
>   		} else {
> -			struct msghdr msg = { .msg_flags = flags };
> -			struct kvec iov = {
> -				.iov_base = segment->data + offset,
> -				.iov_len = copy
> -			};
> -
> -			r = kernel_sendmsg(sk, &msg, &iov, 1, copy);
> +			void *data = segment->data + offset;
> +
> +			/*
> +			 * Make sure it's ok to send the header using zero
> +			 * copy. The case where the sg page can't be zero
> +			 * copied will also go down the sendmsg path.
> +			 */
> +			if (sendpage_ok(data)) {
> +				r = tcp_sw_conn->sendpage(sk,
> +						virt_to_page(data),
> +						offset_in_page(data), copy,
> +						flags);
> +			} else {
> +				struct msghdr msg = { .msg_flags = flags };
> +				struct kvec iov = {
> +					.iov_base = data,
> +					.iov_len = copy,
> +				};
> +
> +				r = kernel_sendmsg(sk, &msg, &iov, 1, copy);
> +			}
>   		}
>   
>   		if (r < 0) {

Reviewed-by: Lee Duncan <lduncan@suse.com>