net: TCP thin-stream detection

index 87d164b..e5e2056 100644
@@ -1386,6 +1386,13 @@ static inline void tcp_highest_sack_combine(struct sock *sk,
 		tcp_sk(sk)->highest_sack = new;
 }
 
+/* Determines whether this is a thin stream (which may suffer from
+ * increased latency). Used to trigger latency-reducing mechanisms.*/
+static inline unsigned int tcp_stream_is_thin(struct tcp_sock *tp)
+{
+	return tp->packets_out < 4 && !tcp_in_initial_slowstart(tp);
+}
+
 /* /proc */
 enum tcp_seq_states {
 	TCP_SEQ_STATE_LISTENING,