[RFC/Review] Prevent network namespace memory exhaution

[John Johansen]

On 03/24/2011 08:00 PM, Tim Gardner wrote:
> On 03/24/2011 09:41 AM, Stefan Bader wrote:
>> BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/720095
>>
>> This series of patches tries to cover a problem that we caught by
>> enabling network namespaces (CONFIG_NET_NS) in Lucid, which was done
>> (although the feature was still marked experimental) to support
>> containerize usecases (and we would get some complaints by
>> removing it now).
>>
>> I tried to come up with some usable solution. Unfortunately picking the
>> minimal set of patches which prevents the memory buildup, also causes the
>> rate of connects (which in that case makes use of network namespace cloning
>> a lot) to go down noticeably.
>>
>> The second half would improve the situation slightly but still not as
>> much as it has been achieved in Maverick. And using the Maverick
>> backport causes other problems in that specific case the bug is
>> reported.
>>
>> To quantify that a bit better:
>>
>> Lucid current        10 connections per second
>> Lucid set 1         1 connection every  2 seconds
>> Lucid set 2         2 connections every 3 seconds
>> Maverick         2 connections per second
>>
>> There has not been a way to verify how bad the impact of the slowdown
>> would be in a real production environment. So it might be a viable
>> approach to limit changes to the first set. Assuming that creating
>> and destroying namespaces is not the common usecase we have.
>>
>> Should there be performance complaints, we still could think of
>> having a closer look at the second set (or more).
>>
>> So generally, does this sound like an approach we can SRU? And
>> second, more eyes looking at the set(s) would be appreciated.
>>
>> -Stefan
>>
>> Those are enough to prevent memory being eaten:
>> * net: Introduce unregister_netdevice_queue()
>> * net: Introduce unregister_netdevice_many()
>> * net: add a list_head parameter to dellink() method
>> * veth: Fix veth_dellink method
>> * veth: Fix unregister_netdevice_queue for veth
>> * net: Implement for_each_netdev_reverse.
>> * net: Batch network namespace destruction.
>>
>> Those seem to speed up the number of connects to vsftp per time (though
>> not as much as Maverick):
>> * net: Automatically allocate per namespace data.
>> * net: Add support for batching network namespace cleanups
>> * netns: Add an explicit rcu_barrier to unregister_pernet_{device|subsys}
>> * net: Use rcu lookups in inet_twsk_purge.
>> * tcp: fix inet_twsk_deschedule()
>> * net: Batch inet_twsk_purge
>>
>> The following changes since commit 054b34d3a38dc2a775ab722411b934b52a33707f:
>>    Brad Figg (1):
>>          UBUNTU: Ubuntu-2.6.32-31.60
>>
>> are available in the git repository at:
>>
>>    git://kernel.ubuntu.com/smb/ubuntu-lucid netnsbpv2
>>
>> Eric Dumazet (5):
>>        net: Introduce unregister_netdevice_queue()
>>        net: Introduce unregister_netdevice_many()
>>        net: add a list_head parameter to dellink() method
>>        veth: Fix veth_dellink method
>>        tcp: fix inet_twsk_deschedule()
>>
>> Eric W. Biederman (8):
>>        veth: Fix unregister_netdevice_queue for veth
>>        net: Implement for_each_netdev_reverse.
>>        net: Batch network namespace destruction.
>>        net: Automatically allocate per namespace data.
>>        net: Add support for batching network namespace cleanups
>>        netns: Add an explicit rcu_barrier to unregister_pernet_{device|subsys}
>>        net: Use rcu lookups in inet_twsk_purge.
>>        net: Batch inet_twsk_purge
>>
>>   drivers/net/macvlan.c            |    6 +-
>>   drivers/net/veth.c               |    6 +-
>>   include/linux/netdevice.h        |   12 ++-
>>   include/net/inet_timewait_sock.h |    6 +-
>>   include/net/net_namespace.h      |   32 ++++-
>>   include/net/rtnetlink.h          |    3 +-
>>   net/8021q/vlan.c                 |    8 +-
>>   net/8021q/vlan.h                 |    2 +-
>>   net/core/dev.c                   |  120 ++++++++++-----
>>   net/core/net_namespace.c         |  296 +++++++++++++++++++++++---------------
>>   net/core/rtnetlink.c             |   14 +-
>>   net/ipv4/inet_timewait_sock.c    |   47 ++++---
>>   net/ipv4/tcp_ipv4.c              |   11 +-
>>   net/ipv6/tcp_ipv6.c              |   11 +-
>>   14 files changed, 369 insertions(+), 205 deletions(-)
>>
> 
> Thats a honking big patch set for an SRU. Its not clear to me from the commit logs, but I assume they are all clean cherry-picks ?
> 
Mostly clean, there are a few minor fixups, for differences that aren't being patched in.  I went through all the patches and they all looked good.

> I'm still not convinced that CONFIG_NET_NS=n isn't the best solution, despite the complaints that change might elicit. I'd like to hear from the consumers of network name spaces about how they are using the feature, and possible workarounds if it were to go away.
> 
That is the solution I would like but I think that at least for the server that is going to be problematic. Container are seeing a lot of use.

If we were to go with an SRU of this I would lean towards the smaller patchset that is enough to prevent memory being eaten (7 of the 13), and then if speed is a problem the remain 6 could be SRUed afterwards.