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 --- Documentation/sysctl/net.txt | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'Documentation') diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt index 35c62f522754..5992602469d8 100644 --- a/Documentation/sysctl/net.txt +++ b/Documentation/sysctl/net.txt @@ -270,6 +270,18 @@ optmem_max Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence of struct cmsghdr structures with appended data. +fb_tunnels_only_for_init_net +---------------------------- + +Controls if fallback tunnels (like tunl0, gre0, gretap0, erspan0, +sit0, ip6tnl0, ip6gre0) are automatically created when a new +network namespace is created, if corresponding tunnel is present +in initial network namespace. +If set to 1, these devices are not automatically created, and +user space is responsible for creating them if needed. + +Default : 0 (for compatibility reasons) + 2. /proc/sys/net/unix - Parameters for Unix domain sockets ------------------------------------------------------- -- cgit v1.2.3