Re: [RFC 0/5] forced comounts for cgroups.

Glauber Costa
2012-09-05T09:35:16Z

On 09/05/2012 01:26 PM, Peter Zijlstra wrote:
> On Wed, 2012-09-05 at 13:12 +0400, Glauber Costa wrote:
>> On 09/05/2012 01:11 PM, Tejun Heo wrote:
>>> Hello, Peter.
>>>
>>> On Wed, Sep 05, 2012 at 11:06:33AM +0200, Peter Zijlstra wrote:
>>>> *confused* I always thought that was exactly what you meant with unified
>>>> hierarchy.
>>>
>>> No, I never counted out differing granularity.
>>>
>>
>> Can you elaborate on which interface do you envision to make it work?
>> They will clearly be mounted in the same hierarchy, or as said
>> alternatively, comounted.
>>
>> If you can turn them on/off on a per-subtree basis, which interface
>> exactly do you propose for that?
>
> I wouldn't, screw that. That would result in the exact same problem
> we're trying to fix. I want a single hierarchy walk, that's expensive
> enough.
>
>> Would a pair of cgroup core files like available_controllers and
>> current_controllers are a lot of drivers do, suffice?
>
> No.. its not a 'feature' I care to support for 'my' controllers.
>
> I simply don't want to have to do two (or more) hierarchy walks for
> accounting on every schedule event, all that pointer chasing is stupidly
> expensive.
>

You wouldn't have to do more than one hierarchy walks for that. What
Tejun seems to want, is the ability to not have a particular controller
at some point in the tree. But if they exist, they are always together.