Merge branch 'tcp_src_port_selection'

Eric Dumazet says:

====================
tcp: improve source port selection

With increase of TCP sockets in hosts, we often hit limitations
caused by port selection, due to randomization and poor strategy.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_hashtables.h

@@ -148,8 +148,6 @@ struct inet_hashinfo {
 	 */
 	struct inet_listen_hashbucket	listening_hash[INET_LHTABLE_SIZE]
 					____cacheline_aligned_in_smp;
-
-	atomic_t			bsockets;
 };
 
 static inline struct inet_ehash_bucket *inet_ehash_bucket(

net/ipv4/inet_connection_sock.c

@@ -99,13 +99,22 @@ int inet_csk_get_port(struct sock *sk, unsigned short snum)
 	struct net *net = sock_net(sk);
 	int smallest_size = -1, smallest_rover;
 	kuid_t uid = sock_i_uid(sk);
+	int attempt_half = (sk->sk_reuse == SK_CAN_REUSE) ? 1 : 0;
 
 	local_bh_disable();
 	if (!snum) {
 		int remaining, rover, low, high;
 
 again:
 		inet_get_local_port_range(net, &low, &high);
+		if (attempt_half) {
+			int half = low + ((high - low) >> 1);
+
+			if (attempt_half == 1)
+				high = half;
+			else
+				low = half;
+		}
 		remaining = (high - low) + 1;
 		smallest_rover = rover = prandom_u32() % remaining + low;
 
@@ -127,11 +136,6 @@ int inet_csk_get_port(struct sock *sk, unsigned short snum)
 					    (tb->num_owners < smallest_size || smallest_size == -1)) {
 						smallest_size = tb->num_owners;
 						smallest_rover = rover;
-						if (atomic_read(&hashinfo->bsockets) > (high - low) + 1 &&
-						    !inet_csk(sk)->icsk_af_ops->bind_conflict(sk, tb, false)) {
-							snum = smallest_rover;
-							goto tb_found;
-						}
 					}
 					if (!inet_csk(sk)->icsk_af_ops->bind_conflict(sk, tb, false)) {
 						snum = rover;
@@ -159,6 +163,11 @@ int inet_csk_get_port(struct sock *sk, unsigned short snum)
 				snum = smallest_rover;
 				goto have_snum;
 			}
+			if (attempt_half == 1) {
+				/* OK we now try the upper half of the range */
+				attempt_half = 2;
+				goto again;
+			}
 			goto fail;
 		}
 		/* OK, here is the one we will use.  HEAD is

net/ipv4/inet_hashtables.c

@@ -90,10 +90,6 @@ void inet_bind_bucket_destroy(struct kmem_cache *cachep, struct inet_bind_bucket
 void inet_bind_hash(struct sock *sk, struct inet_bind_bucket *tb,
 		    const unsigned short snum)
 {
-	struct inet_hashinfo *hashinfo = sk->sk_prot->h.hashinfo;
-
-	atomic_inc(&hashinfo->bsockets);
-
 	inet_sk(sk)->inet_num = snum;
 	sk_add_bind_node(sk, &tb->owners);
 	tb->num_owners++;
@@ -111,8 +107,6 @@ static void __inet_put_port(struct sock *sk)
 	struct inet_bind_hashbucket *head = &hashinfo->bhash[bhash];
 	struct inet_bind_bucket *tb;
 
-	atomic_dec(&hashinfo->bsockets);
-
 	spin_lock(&head->lock);
 	tb = inet_csk(sk)->icsk_bind_hash;
 	__sk_del_bind_node(sk);
@@ -608,7 +602,6 @@ void inet_hashinfo_init(struct inet_hashinfo *h)
 {
 	int i;
 
-	atomic_set(&h->bsockets, 0);
 	for (i = 0; i < INET_LHTABLE_SIZE; i++) {
 		spin_lock_init(&h->listening_hash[i].lock);
 		INIT_HLIST_NULLS_HEAD(&h->listening_hash[i].head,