ipv4: 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        126    282   5504    1    2 : tunables    8    4    0 : slabdata    126    282      0

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

After patch:
$ time ./add_del_unshare.sh
net_namespace        135    291   5504    1    2 : tunables    8    4    0 : slabdata    135    291      0

real	0m22.117s
user	0m0.728s
sys	0m35.328s

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

1 files changed, 3 insertions, 4 deletions

diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
index 5ed63d250950..02d70ca99db1 100644
--- a/net/ipv4/ip_vti.c
+++ b/net/ipv4/ip_vti.c
@@ -452,15 +452,14 @@ static int __net_init vti_init_net(struct net *net)
 	return 0;
 }
 
-static void __net_exit vti_exit_net(struct net *net)
+static void __net_exit vti_exit_batch_net(struct list_head *list_net)
 {
-	struct ip_tunnel_net *itn = net_generic(net, vti_net_id);
-	ip_tunnel_delete_net(itn, &vti_link_ops);
+	ip_tunnel_delete_nets(list_net, vti_net_id, &vti_link_ops);
 }
 
 static struct pernet_operations vti_net_ops = {
 	.init = vti_init_net,
-	.exit = vti_exit_net,
+	.exit_batch = vti_exit_batch_net,
 	.id   = &vti_net_id,
 	.size = sizeof(struct ip_tunnel_net),
 };