[RFC/Review] Prevent network namespace memory exhaution

[Tim Gardner]

On 03/29/2011 11:38 AM, Stefan Bader wrote:
> On 03/29/2011 05:13 PM, Stefan Bader wrote:
>> On 03/29/2011 04:51 PM, Tim Gardner wrote:
>>> 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 ?
>>>
>> Oh well, yeah. Knowingly break something just scares me. But I'll send something
>> out and let the stable guys decide. :-P
>>
>> -Stefan
>>
> So this would be the change to turn them off.
>

applied, pushed

-- 
Tim Gardner tim.gardner at canonical.com