Re: [PATCH net-next v5 11/16] scsi: iscsi_tcp: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage

[Chris Leech]

On Fri, Jun 23, 2023 at 11:55:08PM +0100, David Howells wrote:
> Use sendmsg() with MSG_SPLICE_PAGES rather than sendpage.  This allows
> multiple pages and multipage folios to be passed through.
> 
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> Reviewed-by: Mike Christie <michael.christie@xxxxxxxxxx>
> cc: Lee Duncan <lduncan@xxxxxxxx>
> cc: Chris Leech <cleech@xxxxxxxxxx>
> cc: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxx>
> cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
> cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> cc: Jens Axboe <axboe@xxxxxxxxx>
> cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> cc: open-iscsi@xxxxxxxxxxxxxxxx
> cc: linux-scsi@xxxxxxxxxxxxxxx
> cc: target-devel@xxxxxxxxxxxxxxx
> cc: netdev@xxxxxxxxxxxxxxx
> ---
> 
> Notes:
>     ver #5)
>      - Split iscsi changes into client and target patches
> 
>  drivers/scsi/iscsi_tcp.c | 26 ++++++++++----------------
>  drivers/scsi/iscsi_tcp.h |  2 --
>  2 files changed, 10 insertions(+), 18 deletions(-)

This seems good to me.

Reviewed-by: Chris Leech <cleech@xxxxxxxxxx>
 
> diff --git a/drivers/scsi/iscsi_tcp.c b/drivers/scsi/iscsi_tcp.c
> index 9637d4bc2bc9..9ab8555180a3 100644
> --- a/drivers/scsi/iscsi_tcp.c
> +++ b/drivers/scsi/iscsi_tcp.c
> @@ -301,35 +301,32 @@ static int iscsi_sw_tcp_xmit_segment(struct iscsi_tcp_conn *tcp_conn,
>  
>  	while (!iscsi_tcp_segment_done(tcp_conn, segment, 0, r)) {
>  		struct scatterlist *sg;
> +		struct msghdr msg = {};
> +		struct bio_vec bv;
>  		unsigned int offset, copy;
> -		int flags = 0;
>  
>  		r = 0;
>  		offset = segment->copied;
>  		copy = segment->size - offset;
>  
>  		if (segment->total_copied + segment->size < segment->total_size)
> -			flags |= MSG_MORE | MSG_SENDPAGE_NOTLAST;
> +			msg.msg_flags |= MSG_MORE;
>  
>  		if (tcp_sw_conn->queue_recv)
> -			flags |= MSG_DONTWAIT;
> +			msg.msg_flags |= MSG_DONTWAIT;
>  
> -		/* Use sendpage if we can; else fall back to sendmsg */
>  		if (!segment->data) {
> +			if (!tcp_conn->iscsi_conn->datadgst_en)
> +				msg.msg_flags |= MSG_SPLICE_PAGES;
>  			sg = segment->sg;
>  			offset += segment->sg_offset + sg->offset;
> -			r = tcp_sw_conn->sendpage(sk, sg_page(sg), offset,
> -						  copy, flags);
> +			bvec_set_page(&bv, sg_page(sg), copy, offset);
>  		} 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);
> +			bvec_set_virt(&bv, segment->data + offset, copy);
>  		}
> +		iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bv, 1, copy);
>  
> +		r = sock_sendmsg(sk, &msg);
>  		if (r < 0) {
>  			iscsi_tcp_segment_unmap(segment);
>  			return r;
> @@ -746,7 +743,6 @@ iscsi_sw_tcp_conn_bind(struct iscsi_cls_session *cls_session,
>  	sock_no_linger(sk);
>  
>  	iscsi_sw_tcp_conn_set_callbacks(conn);
> -	tcp_sw_conn->sendpage = tcp_sw_conn->sock->ops->sendpage;
>  	/*
>  	 * set receive state machine into initial state
>  	 */
> @@ -777,8 +773,6 @@ static int iscsi_sw_tcp_conn_set_param(struct iscsi_cls_conn *cls_conn,
>  			return -ENOTCONN;
>  		}
>  		iscsi_set_param(cls_conn, param, buf, buflen);
> -		tcp_sw_conn->sendpage = conn->datadgst_en ?
> -			sock_no_sendpage : tcp_sw_conn->sock->ops->sendpage;
>  		mutex_unlock(&tcp_sw_conn->sock_lock);
>  		break;
>  	case ISCSI_PARAM_MAX_R2T:
> diff --git a/drivers/scsi/iscsi_tcp.h b/drivers/scsi/iscsi_tcp.h
> index 68e14a344904..89a6fc552f0b 100644
> --- a/drivers/scsi/iscsi_tcp.h
> +++ b/drivers/scsi/iscsi_tcp.h
> @@ -47,8 +47,6 @@ struct iscsi_sw_tcp_conn {
>  	/* MIB custom statistics */
>  	uint32_t		sendpage_failures_cnt;
>  	uint32_t		discontiguous_hdr_cnt;
> -
> -	ssize_t (*sendpage)(struct socket *, struct page *, int, size_t, int);
>  };
>  
>  struct iscsi_sw_tcp_host {
>