netdev - [PATCH net-next 04/11] tcp: add receive queue awareness in tcp_rcv_space

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Message-ID: <20250513193919.1089692-5-edumazet@google.com>
Date: Tue, 13 May 2025 19:39:12 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Neal Cardwell <ncardwell@...gle.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...zon.com>, 
	Rick Jones <jonesrick@...gle.com>, Wei Wang <weiwan@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 04/11] tcp: add receive queue awareness in tcp_rcv_space_adjust()

If the application can not drain fast enough a TCP socket queue,
tcp_rcv_space_adjust() can overestimate tp->rcvq_space.space.

Then sk->sk_rcvbuf can grow and hit tcp_rmem[2] for no good reason.

Fix this by taking into acount the number of available bytes.

Keeping sk->sk_rcvbuf at the right size allows better cache efficiency.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reviewed-by: Wei Wang <weiwan@...gle.com>
---
 include/linux/tcp.h  | 2 +-
 net/ipv4/tcp_input.c | 6 ++++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index a8af71623ba7ca16f211cb9884f431fc9462ce9e..29f59d50dc73f8c433865e6bc116cb1bac4eafb7 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -340,7 +340,7 @@ struct tcp_sock {
 	} rcv_rtt_est;
 /* Receiver queue space */
 	struct {
-		u32	space;
+		int	space;
 		u32	seq;
 		u64	time;
 	} rcvq_space;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f799200db26492730fbd042a68c8d206d85455d4..5d64a6ecfc8f78de3665afdea112d62c417cee27 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -780,8 +780,7 @@ static void tcp_rcvbuf_grow(struct sock *sk)
 void tcp_rcv_space_adjust(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
-	u32 copied;
-	int time;
+	int time, inq, copied;
 
 	trace_tcp_rcv_space_adjust(sk);
 
@@ -792,6 +791,9 @@ void tcp_rcv_space_adjust(struct sock *sk)
 
 	/* Number of bytes copied to user in last RTT */
 	copied = tp->copied_seq - tp->rcvq_space.seq;
+	/* Number of bytes in receive queue. */
+	inq = tp->rcv_nxt - tp->copied_seq;
+	copied -= inq;
 	if (copied <= tp->rcvq_space.space)
 		goto new_measure;
 
-- 
2.49.0.1045.g170613ef41-goog