[RFC/Review] Prevent network namespace memory exhaution

[Tim Gardner]

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

rtg
-- 
Tim Gardner tim.gardner at canonical.com