netdev - [PATCH net-next 1/3] tcp: let tcp_send_syn

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Date: Fri,  9 Jun 2023 20:42:44 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 1/3] tcp: let tcp_send_syn_data() build headless packets

tcp_send_syn_data() is the last component in TCP transmit
path to put payload in skb->head.

Switch it to use page frags, so that we can remove dead
code later.

This allows to put more payload than previous implementation.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/tcp.h     |  1 +
 net/ipv4/tcp.c        |  2 +-
 net/ipv4/tcp_output.c | 31 +++++++++++++++++++------------
 3 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 49611af31bb7693cbc18cba61fe8ae2fd1d8695f..f718ed258f07caedca41d01670b1c91fc11e2233 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -333,6 +333,7 @@ int tcp_sendpage(struct sock *sk, struct page *page, int offset, size_t size,
 int tcp_sendpage_locked(struct sock *sk, struct page *page, int offset,
 			size_t size, int flags);
 int tcp_send_mss(struct sock *sk, int *size_goal, int flags);
+int tcp_wmem_schedule(struct sock *sk, int copy);
 void tcp_push(struct sock *sk, int flags, int mss_now, int nonagle,
 	      int size_goal);
 void tcp_release_cb(struct sock *sk);
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 09f03221a6f1597114162360a4c1aeed0758812d..da7f156d9fad93b0ab97cd52bc9e7f9cd3822ea2 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -957,7 +957,7 @@ static int tcp_downgrade_zcopy_pure(struct sock *sk, struct sk_buff *skb)
 }
 
 
-static int tcp_wmem_schedule(struct sock *sk, int copy)
+int tcp_wmem_schedule(struct sock *sk, int copy)
 {
 	int left;
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f8ce77ce7c3ef783717e60cce03d70aa10a4b9a8..d0396633735932857e131709a893b2a811fe4bd6 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3802,8 +3802,9 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct tcp_fastopen_request *fo = tp->fastopen_req;
-	int space, err = 0;
+	struct page_frag *pfrag = sk_page_frag(sk);
 	struct sk_buff *syn_data;
+	int space, err = 0;
 
 	tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
 	if (!tcp_fastopen_cookie_check(sk, &tp->rx_opt.mss_clamp, &fo->cookie))
@@ -3822,25 +3823,31 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
 
 	space = min_t(size_t, space, fo->size);
 
-	/* limit to order-0 allocations */
-	space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
-
-	syn_data = tcp_stream_alloc_skb(sk, space, sk->sk_allocation, false);
+	if (space &&
+	    !skb_page_frag_refill(min_t(size_t, space, PAGE_SIZE),
+				  pfrag, sk->sk_allocation))
+		goto fallback;
+	syn_data = tcp_stream_alloc_skb(sk, 0, sk->sk_allocation, false);
 	if (!syn_data)
 		goto fallback;
 	memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
 	if (space) {
-		int copied = copy_from_iter(skb_put(syn_data, space), space,
-					    &fo->data->msg_iter);
-		if (unlikely(!copied)) {
+		space = min_t(size_t, space, pfrag->size - pfrag->offset);
+		space = tcp_wmem_schedule(sk, space);
+	}
+	if (space) {
+		space = copy_page_from_iter(pfrag->page, pfrag->offset,
+					    space, &fo->data->msg_iter);
+		if (unlikely(!space)) {
 			tcp_skb_tsorted_anchor_cleanup(syn_data);
 			kfree_skb(syn_data);
 			goto fallback;
 		}
-		if (copied != space) {
-			skb_trim(syn_data, copied);
-			space = copied;
-		}
+		skb_fill_page_desc(syn_data, 0, pfrag->page,
+				   pfrag->offset, space);
+		page_ref_inc(pfrag->page);
+		pfrag->offset += space;
+		skb_len_add(syn_data, space);
 		skb_zcopy_set(syn_data, fo->uarg, NULL);
 	}
 	/* No more data pending in inet_wait_for_connect() */
-- 
2.41.0.162.gfafddb0af9-goog