@@ -296,22 +296,14 @@ static void tcp_fixup_sndbuf(struct sock *sk)
  * in common situations. Otherwise, we have to rely on queue collapsing.
  */
 
-/* Slow part of check#2. */
-static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
+/* Slow part of check#2. Estimate a budget for how many bytes of
+ * receive window we can afford to advertise at the current ratio of
+ * skb->len to skb->truesize.
+ */
+static u32 tcp_rcv_ssthresh_budget(const struct sk_buff *skb)
 {
-	struct tcp_sock *tp = tcp_sk(sk);
-	/* Optimize this! */
-	int truesize = tcp_win_from_space(skb->truesize) >> 1;
-	int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
-
-	while (tp->rcv_ssthresh <= window) {
-		if (truesize <= skb->len)
-			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
-
-		truesize >>= 1;
-		window >>= 1;
-	}
-	return 0;
+	u32 skb_budget = sysctl_tcp_rmem[2] / skb->truesize;
+	return (u32) (skb->len * skb_budget);
 }
 
 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)

@@ -322,20 +314,25 @@ static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 	if (tp->rcv_ssthresh < tp->window_clamp &&
 	    (int)tp->rcv_ssthresh < tcp_space(sk) &&
 	    !sk_under_memory_pressure(sk)) {
-		int incr;
-
 		/* Check #2. Increase window, if skb with such overhead
 		 * will fit to rcvbuf in future.
 		 */
-		if (tcp_win_from_space(skb->truesize) <= skb->len)
-			incr = 2 * tp->advmss;
-		else
-			incr = __tcp_grow_window(sk, skb);
+		u32 rcv_ssthresh_budget = tcp_rcv_ssthresh_budget(skb);
+		if (tp->rcv_ssthresh < rcv_ssthresh_budget) {
+			/* With GRO or LRO we may receive an skb of
+			 * many MSS. To enable the sender's cwnd to
+			 * grow at a healthy pace in slow start we
+			 * must open the receive window proportionally
+			 * to skb size.
+			 */
+			u32 incr = skb->len;
 
-		if (incr) {
-			tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
-					       tp->window_clamp);
-			inet_csk(sk)->icsk_ack.quick |= 1;
+			u32 rcv_ssthresh_cap = min(rcv_ssthresh_budget, tp->window_clamp);
+			u32 rcv_ssthresh_now = min(tp->rcv_ssthresh + incr, rcv_ssthresh_cap);
+			if (tp->rcv_ssthresh != rcv_ssthresh_now) {
+				tp->rcv_ssthresh = rcv_ssthresh_now;
+				inet_csk(sk)->icsk_ack.quick |= 1;
+			}
 		}
 	}
 }