linux-kernel - [RFC PATCH 26/28] dlm: Use sendmsg(MSG_SPLICE

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Date:   Thu, 16 Mar 2023 15:26:16 +0000
From:   David Howells <dhowells@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jeff Layton <jlayton@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        netdev@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Christine Caulfield <ccaulfie@...hat.com>,
        David Teigland <teigland@...hat.com>, cluster-devel@...hat.com
Subject: [RFC PATCH 26/28] dlm: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage

When transmitting data, call down a layer using a single sendmsg with
MSG_SPLICE_PAGES to indicate that content should be spliced rather using
sendpage.  This allows ->sendpage() to be replaced by something that can
handle multiple multipage folios in a single transaction.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: Christine Caulfield <ccaulfie@...hat.com>
cc: David Teigland <teigland@...hat.com>
cc: "David S. Miller" <davem@...emloft.net>
cc: Eric Dumazet <edumazet@...gle.com>
cc: Jakub Kicinski <kuba@...nel.org>
cc: Paolo Abeni <pabeni@...hat.com>
cc: Jens Axboe <axboe@...nel.dk>
cc: Matthew Wilcox <willy@...radead.org>
cc: cluster-devel@...hat.com
cc: netdev@...r.kernel.org
---
 fs/dlm/lowcomms.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
index a9b14f81d655..9c0c691b6106 100644
--- a/fs/dlm/lowcomms.c
+++ b/fs/dlm/lowcomms.c
@@ -1394,8 +1394,11 @@ int dlm_lowcomms_resend_msg(struct dlm_msg *msg)
 /* Send a message */
 static int send_to_sock(struct connection *con)
 {
-	const int msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL;
 	struct writequeue_entry *e;
+	struct bio_vec bvec;
+	struct msghdr msg = {
+		.msg_flags = MSG_SPLICE_PAGES | MSG_DONTWAIT | MSG_NOSIGNAL,
+	};
 	int len, offset, ret;
 
 	spin_lock_bh(&con->writequeue_lock);
@@ -1411,8 +1414,9 @@ static int send_to_sock(struct connection *con)
 	WARN_ON_ONCE(len == 0 && e->users == 0);
 	spin_unlock_bh(&con->writequeue_lock);
 
-	ret = kernel_sendpage(con->sock, e->page, offset, len,
-			      msg_flags);
+	bvec_set_page(&bvec, e->page, len, offset);
+	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, len);
+	ret = sock_sendmsg(con->sock, &msg);
 	trace_dlm_send(con->nodeid, ret);
 	if (ret == -EAGAIN || ret == 0) {
 		lock_sock(con->sock->sk);