Re: [RFC PATCH v2 40/48] sunrpc: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage

[Chuck Lever III <chuck.lever@oracle.com>]

> On Mar 30, 2023, at 10:26 AM, David Howells <dhowells@redhat.com> wrote:
> 
> Chuck Lever III <chuck.lever@oracle.com> wrote:
> 
>> Don't. Just change svc_tcp_send_kvec() to use sock_sendmsg, and
>> leave the marker alone for now, please.
> 
> If you insist.  See attached.

Very good, thank you for accommodating my regression paranoia.

Acked-by: Chuck Lever <chuck.lever@oracle.com>


> 
> David
> ---
> sunrpc: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage
> 
> When transmitting data, call down into TCP using sendmsg with
> MSG_SPLICE_PAGES to indicate that content should be spliced rather than
> performing sendpage calls to transmit header, data pages and trailer.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Trond Myklebust <trond.myklebust@hammerspace.com>
> cc: Anna Schumaker <anna@kernel.org>
> cc: Chuck Lever <chuck.lever@oracle.com>
> cc: Jeff Layton <jlayton@kernel.org>
> cc: "David S. Miller" <davem@davemloft.net>
> cc: Eric Dumazet <edumazet@google.com>
> cc: Jakub Kicinski <kuba@kernel.org>
> cc: Paolo Abeni <pabeni@redhat.com>
> cc: Jens Axboe <axboe@kernel.dk>
> cc: Matthew Wilcox <willy@infradead.org>
> cc: linux-nfs@vger.kernel.org
> cc: netdev@vger.kernel.org
> ---
> include/linux/sunrpc/svc.h |   11 +++++------
> net/sunrpc/svcsock.c       |   40 +++++++++++++---------------------------
> 2 files changed, 18 insertions(+), 33 deletions(-)
> 
> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> index 877891536c2f..456ae554aa11 100644
> --- a/include/linux/sunrpc/svc.h
> +++ b/include/linux/sunrpc/svc.h
> @@ -161,16 +161,15 @@ static inline bool svc_put_not_last(struct svc_serv *serv)
> extern u32 svc_max_payload(const struct svc_rqst *rqstp);
> 
> /*
> - * RPC Requsts and replies are stored in one or more pages.
> + * RPC Requests and replies are stored in one or more pages.
>  * We maintain an array of pages for each server thread.
>  * Requests are copied into these pages as they arrive.  Remaining
>  * pages are available to write the reply into.
>  *
> - * Pages are sent using ->sendpage so each server thread needs to
> - * allocate more to replace those used in sending.  To help keep track
> - * of these pages we have a receive list where all pages initialy live,
> - * and a send list where pages are moved to when there are to be part
> - * of a reply.
> + * Pages are sent using ->sendmsg with MSG_SPLICE_PAGES so each server thread
> + * needs to allocate more to replace those used in sending.  To help keep track
> + * of these pages we have a receive list where all pages initialy live, and a
> + * send list where pages are moved to when there are to be part of a reply.
>  *
>  * We use xdr_buf for holding responses as it fits well with NFS
>  * read responses (that have a header, and some data pages, and possibly
> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
> index 03a4f5615086..af146e053dfc 100644
> --- a/net/sunrpc/svcsock.c
> +++ b/net/sunrpc/svcsock.c
> @@ -1059,17 +1059,18 @@ static int svc_tcp_recvfrom(struct svc_rqst *rqstp)
> 	svc_xprt_received(rqstp->rq_xprt);
> 	return 0;	/* record not complete */
> }
> -
> + 
> static int svc_tcp_send_kvec(struct socket *sock, const struct kvec *vec,
> 			      int flags)
> {
> -	return kernel_sendpage(sock, virt_to_page(vec->iov_base),
> -			       offset_in_page(vec->iov_base),
> -			       vec->iov_len, flags);
> +	struct msghdr msg = { .msg_flags = MSG_SPLICE_PAGES | flags, };
> +
> +	iov_iter_kvec(&msg.msg_iter, ITER_SOURCE, vec, 1, vec->iov_len);
> +	return sock_sendmsg(sock, &msg);
> }
> 
> /*
> - * kernel_sendpage() is used exclusively to reduce the number of
> + * MSG_SPLICE_PAGES is used exclusively to reduce the number of
>  * copy operations in this path. Therefore the caller must ensure
>  * that the pages backing @xdr are unchanging.
>  *
> @@ -1109,28 +1110,13 @@ static int svc_tcp_sendmsg(struct socket *sock, struct xdr_buf *xdr,
> 	if (ret != head->iov_len)
> 		goto out;
> 
> -	if (xdr->page_len) {
> -		unsigned int offset, len, remaining;
> -		struct bio_vec *bvec;
> -
> -		bvec = xdr->bvec + (xdr->page_base >> PAGE_SHIFT);
> -		offset = offset_in_page(xdr->page_base);
> -		remaining = xdr->page_len;
> -		while (remaining > 0) {
> -			len = min(remaining, bvec->bv_len - offset);
> -			ret = kernel_sendpage(sock, bvec->bv_page,
> -					      bvec->bv_offset + offset,
> -					      len, 0);
> -			if (ret < 0)
> -				return ret;
> -			*sentp += ret;
> -			if (ret != len)
> -				goto out;
> -			remaining -= len;
> -			offset = 0;
> -			bvec++;
> -		}
> -	}
> +	msg.msg_flags = MSG_SPLICE_PAGES;
> +	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, xdr->bvec,
> +		      xdr_buf_pagecount(xdr), xdr->page_len);
> +	ret = sock_sendmsg(sock, &msg);
> +	if (ret < 0)
> +		return ret;
> +	*sentp += ret;
> 
> 	if (tail->iov_len) {
> 		ret = svc_tcp_send_kvec(sock, tail, 0);
> 

--
Chuck Lever