tcp: up initial rmem to 128KB and SYN rwin to around 64KB

Previously TCP initial receive buffer is ~87KB by default and
the initial receive window is ~29KB (20 MSS). This patch changes
the two numbers to 128KB and ~64KB (rounding down to the multiples
of MSS) respectively. The patch also simplifies the calculations s.t.
the two numbers are directly controlled by sysctl tcp_rmem[1]:

  1) Initial receiver buffer budget (sk_rcvbuf): while this should
     be configured via sysctl tcp_rmem[1], previously tcp_fixup_rcvbuf()
     always override and set a larger size when a new connection
     establishes.

  2) Initial receive window in SYN: previously it is set to 20
     packets if MSS <= 1460. The number 20 was based on the initial
     congestion window of 10: the receiver needs twice amount to
     avoid being limited by the receive window upon out-of-order
     delivery in the first window burst. But since this only
     applies if the receiving MSS <= 1460, connection using large MTU
     (e.g. to utilize receiver zero-copy) may be limited by the
     receive window.

With this patch TCP memory configuration is more straight-forward and
more properly sized to modern high-speed networks by default. Several
popular stacks have been announcing 64KB rwin in SYNs as well.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 23 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d703a0b3b6a2..7a59f6a96212 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -426,26 +426,7 @@ static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 	}
 }
 
-/* 3. Tuning rcvbuf, when connection enters established state. */
-static void tcp_fixup_rcvbuf(struct sock *sk)
-{
-	u32 mss = tcp_sk(sk)->advmss;
-	int rcvmem;
-
-	rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) *
-		 tcp_default_init_rwnd(mss);
-
-	/* Dynamic Right Sizing (DRS) has 2 to 3 RTT latency
-	 * Allow enough cushion so that sender is not limited by our window
-	 */
-	if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf)
-		rcvmem <<= 2;
-
-	if (sk->sk_rcvbuf < rcvmem)
-		sk->sk_rcvbuf = min(rcvmem, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
-}
-
-/* 4. Try to fixup all. It is made immediately after connection enters
+/* 3. Try to fixup all. It is made immediately after connection enters
  *    established state.
  */
 void tcp_init_buffer_space(struct sock *sk)
@@ -454,8 +435,6 @@ void tcp_init_buffer_space(struct sock *sk)
 	struct tcp_sock *tp = tcp_sk(sk);
 	int maxwin;
 
-	if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
-		tcp_fixup_rcvbuf(sk);
 	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
 		tcp_sndbuf_expand(sk);
 
@@ -485,7 +464,7 @@ void tcp_init_buffer_space(struct sock *sk)
 	tp->snd_cwnd_stamp = tcp_jiffies32;
 }
 
-/* 5. Recalculate window clamp after socket hit its memory bounds. */
+/* 4. Recalculate window clamp after socket hit its memory bounds. */
 static void tcp_clamp_window(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);