net/smc: Cork when sendpage with MSG_SENDPAGE_NOTLAST flag

This introduces a new corked flag, MSG_SENDPAGE_NOTLAST, which is
involved in syscall sendfile() [1], it indicates this is not the last
page. So we can cork the data until the page is not specify this flag.
It has the same effect as MSG_MORE, but existed in sendfile() only.

This patch adds a option MSG_SENDPAGE_NOTLAST for corking data, try to
cork more data before sending when using sendfile(), which acts like
TCP's behaviour. Also, this reimplements the default sendpage to inform
that it is supported to some extent.

[1] https://man7.org/linux/man-pages/man2/sendfile.2.htmlSigned-off-by: Tony Lu <tonylu@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/smc/af_smc.c

@@ -2662,8 +2662,10 @@ static ssize_t smc_sendpage(struct socket *sock, struct page *page,
 		rc = kernel_sendpage(smc->clcsock, page, offset,
 				     size, flags);
 	} else {
+		lock_sock(sk);
+		rc = smc_tx_sendpage(smc, page, offset, size, flags);
+		release_sock(sk);
 		SMC_STAT_INC(smc, sendpage_cnt);
-		rc = sock_no_sendpage(sock, page, offset, size, flags);
 	}
 
 out:

net/smc/smc_tx.c

@@ -235,7 +235,8 @@ int smc_tx_sendmsg(struct smc_sock *smc, struct msghdr *msg, size_t len)
 		 */
 		if ((msg->msg_flags & MSG_OOB) && !send_remaining)
 			conn->urg_tx_pend = true;
-		if ((msg->msg_flags & MSG_MORE || smc_tx_is_corked(smc)) &&
+		if ((msg->msg_flags & MSG_MORE || smc_tx_is_corked(smc) ||
+		     msg->msg_flags & MSG_SENDPAGE_NOTLAST) &&
 		    (atomic_read(&conn->sndbuf_space)))
 			/* for a corked socket defer the RDMA writes if
 			 * sndbuf_space is still available. The applications
@@ -257,6 +258,22 @@ int smc_tx_sendmsg(struct smc_sock *smc, struct msghdr *msg, size_t len)
 	return rc;
 }
 
+int smc_tx_sendpage(struct smc_sock *smc, struct page *page, int offset,
+		    size_t size, int flags)
+{
+	struct msghdr msg = {.msg_flags = flags};
+	char *kaddr = kmap(page);
+	struct kvec iov;
+	int rc;
+
+	iov.iov_base = kaddr + offset;
+	iov.iov_len = size;
+	iov_iter_kvec(&msg.msg_iter, WRITE, &iov, 1, size);
+	rc = smc_tx_sendmsg(smc, &msg, size);
+	kunmap(page);
+	return rc;
+}
+
 /***************************** sndbuf consumer *******************************/
 
 /* sndbuf consumer: actual data transfer of one target chunk with ISM write */

net/smc/smc_tx.h

@@ -31,6 +31,8 @@ void smc_tx_pending(struct smc_connection *conn);
 void smc_tx_work(struct work_struct *work);
 void smc_tx_init(struct smc_sock *smc);
 int smc_tx_sendmsg(struct smc_sock *smc, struct msghdr *msg, size_t len);
+int smc_tx_sendpage(struct smc_sock *smc, struct page *page, int offset,
+		    size_t size, int flags);
 int smc_tx_sndbuf_nonempty(struct smc_connection *conn);
 void smc_tx_sndbuf_nonfull(struct smc_sock *smc);
 void smc_tx_consumer_update(struct smc_connection *conn, bool force);