[PATCH net-next] tcp: use TCP_DEFAULT_INIT_RCVWND in tcp_fixup_rcvbuf()

[Eric Dumazet <eric.dumazet@gmail.com>]

Since commit 356f039822b (TCP: increase default initial receive
window.), we allow sender to send 10 (TCP_DEFAULT_INIT_RCVWND) segments.

Change tcp_fixup_rcvbuf() to reflect this change, even if no real change 
is expected, since sysctl_tcp_rmem[1] = 87380 and this value
is bigger than tcp_fixup_rcvbuf() computed rcvmem (~23720)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
 net/ipv4/tcp_input.c |   16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 1e848b2..5a29ecc 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -345,17 +345,15 @@ static void tcp_grow_window(struct sock *sk, struct sk_buff *skb)
 
 static void tcp_fixup_rcvbuf(struct sock *sk)
 {
-	struct tcp_sock *tp = tcp_sk(sk);
-	int rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
+	const struct tcp_sock *tp = tcp_sk(sk);
+	unsigned int mss = min_t(unsigned int, tp->advmss, 1460);
+	int rcvmem = SKB_TRUESIZE(mss + MAX_TCP_HEADER);
 
-	/* Try to select rcvbuf so that 4 mss-sized segments
-	 * will fit to window and corresponding skbs will fit to our rcvbuf.
-	 * (was 3; 4 is minimum to allow fast retransmit to work.)
-	 */
-	while (tcp_win_from_space(rcvmem) < tp->advmss)
+	while (tcp_win_from_space(rcvmem) < mss)
 		rcvmem += 128;
-	if (sk->sk_rcvbuf < 4 * rcvmem)
-		sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
+	rcvmem *= TCP_DEFAULT_INIT_RCVWND;
+	if (sk->sk_rcvbuf < rcvmem)
+		sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
 }
 
 /* 4. Try to fixup all. It is made immediately after connection enters