From 79134e6ce2c9d1a00eab4d98cb48f975dd2474cb Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 8 Mar 2018 12:51:41 -0800 Subject: net: do not create fallback tunnels for non-default namespaces fallback tunnels (like tunl0, gre0, gretap0, erspan0, sit0, ip6tnl0, ip6gre0) are automatically created when the corresponding module is loaded. These tunnels are also automatically created when a new network namespace is created, at a great cost. In many cases, netns are used for isolation purposes, and these extra network devices are a waste of resources. We are using thousands of netns per host, and hit the netns creation/delete bottleneck a lot. (Many thanks to Kirill for recent work on this) Add a new sysctl so that we can opt-out from this automatic creation. Note that these tunnels are still created for the initial namespace, to be the least intrusive for typical setups. Tested: lpk43:~# 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 lpk43:~# echo 0 >/proc/sys/net/core/fb_tunnels_only_for_init_net lpk43:~# time ./add_del_unshare.sh real 0m37.521s user 0m0.886s sys 7m7.084s lpk43:~# echo 1 >/proc/sys/net/core/fb_tunnels_only_for_init_net lpk43:~# time ./add_del_unshare.sh real 0m4.761s user 0m0.851s sys 1m8.343s lpk43:~# Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv6/sit.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'net/ipv6/sit.c') diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c index a9c4ac6efe22..8a4f8fddd812 100644 --- a/net/ipv6/sit.c +++ b/net/ipv6/sit.c @@ -182,7 +182,7 @@ static void ipip6_tunnel_clone_6rd(struct net_device *dev, struct sit_net *sitn) #ifdef CONFIG_IPV6_SIT_6RD struct ip_tunnel *t = netdev_priv(dev); - if (dev == sitn->fb_tunnel_dev) { + if (dev == sitn->fb_tunnel_dev || !sitn->fb_tunnel_dev) { ipv6_addr_set(&t->ip6rd.prefix, htonl(0x20020000), 0, 0, 0); t->ip6rd.relay_prefix = 0; t->ip6rd.prefixlen = 16; @@ -1835,6 +1835,9 @@ static int __net_init sit_init_net(struct net *net) sitn->tunnels[2] = sitn->tunnels_r; sitn->tunnels[3] = sitn->tunnels_r_l; + if (!net_has_fallback_tunnels(net)) + return 0; + sitn->fb_tunnel_dev = alloc_netdev(sizeof(struct ip_tunnel), "sit0", NET_NAME_UNKNOWN, ipip6_tunnel_setup); -- cgit v1.2.3-59-g8ed1b