[RFC/Review] Prevent network namespace memory exhaution

[Tim Gardner]

On 03/28/2011 02:05 AM, Stefan Bader wrote:
> On 03/25/2011 03:43 PM, John Johansen wrote:
>> On 03/25/2011 07:36 AM, Tim Gardner wrote:
>>> On 03/25/2011 08:30 AM, John Johansen wrote:
>>>> On 03/25/2011 06:49 AM, Tim Gardner wrote:
>>>>> On 03/25/2011 07:16 AM, John Johansen wrote:
>>>>>
>>>>>>> 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.
>>>>>>
>>>>>
>>>>> While containers in general are in use, are network name spaces
>>>>> pro-actively being used? Is there some workload that is _dependent_
>>>>> on NET_NS ? I'm not proposing that we disable containers or other
>>>>> name space features, only NET_NS.
>>>>>
>>>> I don't know the answer to that, it is worth exploring.  It is
>>>> pro-actively being used in that some applications are requesting the
>>>> CLONE_NEWNET flag, and I have seen container workloads that could
>>>> claim to require NET_NS (essentially replacing virtual machines with
>>>> containers) but I am not sure what kernel they were using.  I
>>>> actually would like to turn NET_NS off too, my concern is that it is
>>>> a regression of the feature that some (unquantifiable) set of users
>>>> are using.
>>>>
>>>>>> 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.
>>>>>
>>>>> I'm not keen on releasing a kernel that reduces connection
>>>>> setup/teardown by an order of magnitude. Surely this'll have an
>>>>> adverse impact on web servers and the like.
>>>>>
>>>> Neither am I but, but my perhaps flawed understanding was it should
>>>> only affect the connection setup/teardown if a new network namespace
>>>> is being created, and I doubt most use cases actually do this.  This
>>>> is actually something we should get a better handle on, what work
>>>> loads that use NET_NS are noticeably impacted by this.
>>>
>>> Well, there is an alternative for those folks that _are_ dependent on NET_NS:
>>>
>>> sudo apt-get install linux-image-server-lts-backport-maverick
>>>
>> oh right, that convinces me.  Turn it off.
>
> Sorry for stepping back into this discussion late. I think as long as it ok to
> go with a Maverick kernel, this clearly would be better than any partial
> backport for NET_NS. At least in the one specific case it was suggested that
> doing this was (at least for the moment) not possible as Maverick caused other
> problems. There was however only very vague hints about what those other
> problems really are, so it is hard to tell whether and how those could be solved.
>
> Just for the record, it is my understanding (as John already mentioned) that the
> slowdown only affects connections made with network namspace cloning involved.
> If that feature is not used, there should be no real slowdown.
>
> Summarizing, I think the safest solution is to turn the feature off. But we need
> to be careful about it. This being a LTS release there could also be people
> using it and for various reasons (sw cert) not be able to move to a newer kernel
> that simple. Unfortunately it is hard to find out before doing.
>
> -Stefan

So, are you gonna send a patch disabling NET_NS ?

-- 
Tim Gardner tim.gardner at canonical.com