Merge branch 'net-speedup-netns-create-delete-time'

Eric Dumazet says:

====================
net: speedup netns create/delete time

When rate of netns creation/deletion is high enough,
we observe softlockups in cleanup_net() caused by huge list
of netns and way too many rcu_barrier() calls.

This patch series does some optimizations in kobject,
and add batching to tunnels so that netns dismantles are
less costly.

IPv6 addrlabels also get a per netns list, and tcp_metrics
also benefit from batch flushing.

This gives me one order of magnitude gain.
(~50 ms -> ~5 ms for one netns create/delete pair)

Tested:

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 series :

$ time ./add_del_unshare.sh
net_namespace        116    258   5504    1    2 : tunables    8    4    0 : slabdata    116    258      0

real	3m24.910s
user	0m0.747s
sys	0m43.162s

After :
$ 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: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 5 deletions

diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index 102b2c90bb80..0ab78abc811b 100644
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -892,10 +892,14 @@ static void tcp_metrics_flush_all(struct net *net)
 
 	for (row = 0; row < max_rows; row++, hb++) {
 		struct tcp_metrics_block __rcu **pp;
+		bool match;
+
 		spin_lock_bh(&tcp_metrics_lock);
 		pp = &hb->chain;
 		for (tm = deref_locked(*pp); tm; tm = deref_locked(*pp)) {
-			if (net_eq(tm_net(tm), net)) {
+			match = net ? net_eq(tm_net(tm), net) :
+				!atomic_read(&tm_net(tm)->count);
+			if (match) {
 				*pp = tm->tcpm_next;
 				kfree_rcu(tm, rcu_head);
 			} else {
@@ -1018,14 +1022,14 @@ static int __net_init tcp_net_metrics_init(struct net *net)
 	return 0;
 }
 
-static void __net_exit tcp_net_metrics_exit(struct net *net)
+static void __net_exit tcp_net_metrics_exit_batch(struct list_head *net_exit_list)
 {
-	tcp_metrics_flush_all(net);
+	tcp_metrics_flush_all(NULL);
 }
 
 static __net_initdata struct pernet_operations tcp_net_metrics_ops = {
-	.init	=	tcp_net_metrics_init,
-	.exit	=	tcp_net_metrics_exit,
+	.init		=	tcp_net_metrics_init,
+	.exit_batch	=	tcp_net_metrics_exit_batch,
 };
 
 void __init tcp_metrics_init(void)