netfilter: nf_conntrack: speed up module removal path if netns in use

The patch introduces nf_conntrack_cleanup_net_list(), which cleanups
nf_conntrack for a list of netns and calls synchronize_net() only once
for them all. This should reduce netns destruction time.

I've measured cleanup time for 1k dummy net ns. Here are the results:

 <without the patch>
 # modprobe nf_conntrack
 # time modprobe -r nf_conntrack

 real	0m10.337s
 user	0m0.000s
 sys	0m0.376s

 <with the patch>
 # modprobe nf_conntrack
 # time modprobe -r nf_conntrack

 real    0m5.661s
 user    0m0.000s
 sys     0m0.216s

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Patrick McHardy <kaber@trash.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 10 insertions, 6 deletions

diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index 6bcce401fd1c5..6c69fbdb8361a 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -545,16 +545,20 @@ out_init:
 	return ret;
 }
 
-static void nf_conntrack_pernet_exit(struct net *net)
+static void nf_conntrack_pernet_exit(struct list_head *net_exit_list)
 {
-	nf_conntrack_standalone_fini_sysctl(net);
-	nf_conntrack_standalone_fini_proc(net);
-	nf_conntrack_cleanup_net(net);
+	struct net *net;
+
+	list_for_each_entry(net, net_exit_list, exit_list) {
+		nf_conntrack_standalone_fini_sysctl(net);
+		nf_conntrack_standalone_fini_proc(net);
+	}
+	nf_conntrack_cleanup_net_list(net_exit_list);
 }
 
 static struct pernet_operations nf_conntrack_net_ops = {
-	.init = nf_conntrack_pernet_init,
-	.exit = nf_conntrack_pernet_exit,
+	.init		= nf_conntrack_pernet_init,
+	.exit_batch	= nf_conntrack_pernet_exit,
 };
 
 static int __init nf_conntrack_standalone_init(void)