ipv6: speedup ipv6 tunnels dismantle

Implement exit_batch() method to dismantle more devices
per round.

(rtnl_lock() ...
 unregister_netdevice_many() ...
 rtnl_unlock())

Tested:
$ cat add_del_unshare.sh
for i in `seq 1 40`
do
 (for j in `seq 1 100` ; do unshare -n /bin/true >/dev/null ; done) &
done
wait ; grep net_namespace /proc/slabinfo

Before patch :
$ time ./add_del_unshare.sh
net_namespace        110    267   5504    1    2 : tunables    8    4    0 : slabdata    110    267      0

real    3m25.292s
user    0m0.644s
sys     0m40.153s

After patch:

$ time ./add_del_unshare.sh
net_namespace        126    282   5504    1    2 : tunables    8    4    0 : slabdata    126    282      0

real	1m38.965s
user	0m0.688s
sys	0m37.017s

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_gre.c

@@ -1155,19 +1155,21 @@ err_alloc_dev:
 	return err;
 }
 
-static void __net_exit ip6gre_exit_net(struct net *net)
+static void __net_exit ip6gre_exit_batch_net(struct list_head *net_list)
 {
+	struct net *net;
 	LIST_HEAD(list);
 
 	rtnl_lock();
-	ip6gre_destroy_tunnels(net, &list);
+	list_for_each_entry(net, net_list, exit_list)
+		ip6gre_destroy_tunnels(net, &list);
 	unregister_netdevice_many(&list);
 	rtnl_unlock();
 }
 
 static struct pernet_operations ip6gre_net_ops = {
 	.init = ip6gre_init_net,
-	.exit = ip6gre_exit_net,
+	.exit_batch = ip6gre_exit_batch_net,
 	.id   = &ip6gre_net_id,
 	.size = sizeof(struct ip6gre_net),
 };

net/ipv6/ip6_tunnel.c

@@ -2167,17 +2167,16 @@ static struct xfrm6_tunnel ip6ip6_handler __read_mostly = {
 	.priority	=	1,
 };
 
-static void __net_exit ip6_tnl_destroy_tunnels(struct net *net)
+static void __net_exit ip6_tnl_destroy_tunnels(struct net *net, struct list_head *list)
 {
 	struct ip6_tnl_net *ip6n = net_generic(net, ip6_tnl_net_id);
 	struct net_device *dev, *aux;
 	int h;
 	struct ip6_tnl *t;
-	LIST_HEAD(list);
 
 	for_each_netdev_safe(net, dev, aux)
 		if (dev->rtnl_link_ops == &ip6_link_ops)
-			unregister_netdevice_queue(dev, &list);
+			unregister_netdevice_queue(dev, list);
 
 	for (h = 0; h < IP6_TUNNEL_HASH_SIZE; h++) {
 		t = rtnl_dereference(ip6n->tnls_r_l[h]);
@@ -2186,12 +2185,10 @@ static void __net_exit ip6_tnl_destroy_tunnels(struct net *net)
 			 * been added to the list by the previous loop.
 			 */
 			if (!net_eq(dev_net(t->dev), net))
-				unregister_netdevice_queue(t->dev, &list);
+				unregister_netdevice_queue(t->dev, list);
 			t = rtnl_dereference(t->next);
 		}
 	}
-
-	unregister_netdevice_many(&list);
 }
 
 static int __net_init ip6_tnl_init_net(struct net *net)
@@ -2235,16 +2232,21 @@ err_alloc_dev:
 	return err;
 }
 
-static void __net_exit ip6_tnl_exit_net(struct net *net)
+static void __net_exit ip6_tnl_exit_batch_net(struct list_head *net_list)
 {
+	struct net *net;
+	LIST_HEAD(list);
+
 	rtnl_lock();
-	ip6_tnl_destroy_tunnels(net);
+	list_for_each_entry(net, net_list, exit_list)
+		ip6_tnl_destroy_tunnels(net, &list);
+	unregister_netdevice_many(&list);
 	rtnl_unlock();
 }
 
 static struct pernet_operations ip6_tnl_net_ops = {
 	.init = ip6_tnl_init_net,
-	.exit = ip6_tnl_exit_net,
+	.exit_batch = ip6_tnl_exit_batch_net,
 	.id   = &ip6_tnl_net_id,
 	.size = sizeof(struct ip6_tnl_net),
 };

net/ipv6/ip6_vti.c

@@ -1052,23 +1052,22 @@ static struct rtnl_link_ops vti6_link_ops __read_mostly = {
 	.get_link_net	= ip6_tnl_get_link_net,
 };
 
-static void __net_exit vti6_destroy_tunnels(struct vti6_net *ip6n)
+static void __net_exit vti6_destroy_tunnels(struct vti6_net *ip6n,
+					    struct list_head *list)
 {
 	int h;
 	struct ip6_tnl *t;
-	LIST_HEAD(list);
 
 	for (h = 0; h < IP6_VTI_HASH_SIZE; h++) {
 		t = rtnl_dereference(ip6n->tnls_r_l[h]);
 		while (t) {
-			unregister_netdevice_queue(t->dev, &list);
+			unregister_netdevice_queue(t->dev, list);
 			t = rtnl_dereference(t->next);
 		}
 	}
 
 	t = rtnl_dereference(ip6n->tnls_wc[0]);
-	unregister_netdevice_queue(t->dev, &list);
-	unregister_netdevice_many(&list);
+	unregister_netdevice_queue(t->dev, list);
 }
 
 static int __net_init vti6_init_net(struct net *net)
@@ -1108,18 +1107,24 @@ err_alloc_dev:
 	return err;
 }
 
-static void __net_exit vti6_exit_net(struct net *net)
+static void __net_exit vti6_exit_batch_net(struct list_head *net_list)
 {
-	struct vti6_net *ip6n = net_generic(net, vti6_net_id);
+	struct vti6_net *ip6n;
+	struct net *net;
+	LIST_HEAD(list);
 
 	rtnl_lock();
-	vti6_destroy_tunnels(ip6n);
+	list_for_each_entry(net, net_list, exit_list) {
+		ip6n = net_generic(net, vti6_net_id);
+		vti6_destroy_tunnels(ip6n, &list);
+	}
+	unregister_netdevice_many(&list);
 	rtnl_unlock();
 }
 
 static struct pernet_operations vti6_net_ops = {
 	.init = vti6_init_net,
-	.exit = vti6_exit_net,
+	.exit_batch = vti6_exit_batch_net,
 	.id   = &vti6_net_id,
 	.size = sizeof(struct vti6_net),
 };

net/ipv6/sit.c

@@ -1848,19 +1848,22 @@ err_alloc_dev:
 	return err;
 }
 
-static void __net_exit sit_exit_net(struct net *net)
+static void __net_exit sit_exit_batch_net(struct list_head *net_list)
 {
 	LIST_HEAD(list);
+	struct net *net;
 
 	rtnl_lock();
-	sit_destroy_tunnels(net, &list);
+	list_for_each_entry(net, net_list, exit_list)
+		sit_destroy_tunnels(net, &list);
+
 	unregister_netdevice_many(&list);
 	rtnl_unlock();
 }
 
 static struct pernet_operations sit_net_ops = {
 	.init = sit_init_net,
-	.exit = sit_exit_net,
+	.exit_batch = sit_exit_batch_net,
 	.id   = &sit_net_id,
 	.size = sizeof(struct sit_net),
 };