linux-kernel - [RFC net-next v3 11/29] tcp: support zc with managed data

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Date:   Tue, 28 Jun 2022 19:56:33 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     io-uring@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jens Axboe <axboe@...nel.dk>, kernel-team@...com,
        Pavel Begunkov <asml.silence@...il.com>
Subject: [RFC net-next v3 11/29] tcp: support zc with managed data

Also make tcp to use managed data and propagate SKBFL_MANAGED_FRAG_REFS
to optimise frag pages referencing.

Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 net/ipv4/tcp.c | 51 +++++++++++++++++++++++++++++++++-----------------
 1 file changed, 34 insertions(+), 17 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 9984d23a7f3e..832c1afcdbe7 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1202,17 +1202,23 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 
 	flags = msg->msg_flags;
 
-	if (flags & MSG_ZEROCOPY && size && sock_flag(sk, SOCK_ZEROCOPY)) {
+	if ((flags & MSG_ZEROCOPY) && size) {
 		skb = tcp_write_queue_tail(sk);
-		uarg = msg_zerocopy_realloc(sk, size, skb_zcopy(skb));
-		if (!uarg) {
-			err = -ENOBUFS;
-			goto out_err;
-		}
 
-		zc = sk->sk_route_caps & NETIF_F_SG;
-		if (!zc)
-			uarg->zerocopy = 0;
+		if (msg->msg_ubuf) {
+			uarg = msg->msg_ubuf;
+			net_zcopy_get(uarg);
+			zc = sk->sk_route_caps & NETIF_F_SG;
+		} else if (sock_flag(sk, SOCK_ZEROCOPY)) {
+			uarg = msg_zerocopy_realloc(sk, size, skb_zcopy(skb));
+			if (!uarg) {
+				err = -ENOBUFS;
+				goto out_err;
+			}
+			zc = sk->sk_route_caps & NETIF_F_SG;
+			if (!zc)
+				uarg->zerocopy = 0;
+		}
 	}
 
 	if (unlikely(flags & MSG_FASTOPEN || inet_sk(sk)->defer_connect) &&
@@ -1335,8 +1341,13 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 
 			copy = min_t(int, copy, pfrag->size - pfrag->offset);
 
-			if (tcp_downgrade_zcopy_pure(sk, skb) ||
-			    !sk_wmem_schedule(sk, copy))
+			if (unlikely(skb_zcopy_pure(skb) || skb_zcopy_managed(skb))) {
+				if (tcp_downgrade_zcopy_pure(sk, skb))
+					goto wait_for_space;
+				skb_zcopy_downgrade_managed(skb);
+			}
+
+			if (!sk_wmem_schedule(sk, copy))
 				goto wait_for_space;
 
 			err = skb_copy_to_page_nocache(sk, &msg->msg_iter, skb,
@@ -1357,14 +1368,20 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 			pfrag->offset += copy;
 		} else {
 			/* First append to a fragless skb builds initial
-			 * pure zerocopy skb
+			 * zerocopy skb
 			 */
-			if (!skb->len)
+			if (!skb->len) {
+				if (msg->msg_managed_data)
+					skb_shinfo(skb)->flags |= SKBFL_MANAGED_FRAG_REFS;
 				skb_shinfo(skb)->flags |= SKBFL_PURE_ZEROCOPY;
-
-			if (!skb_zcopy_pure(skb)) {
-				if (!sk_wmem_schedule(sk, copy))
-					goto wait_for_space;
+			} else {
+				/* appending, don't mix managed and unmanaged */
+				if (!msg->msg_managed_data)
+					skb_zcopy_downgrade_managed(skb);
+				if (!skb_zcopy_pure(skb)) {
+					if (!sk_wmem_schedule(sk, copy))
+						goto wait_for_space;
+				}
 			}
 
 			err = skb_zerocopy_iter_stream(sk, skb, msg, copy, uarg);
-- 
2.36.1