[PATCH REPOST RFC cgroup/for-3.7] cgroup: mark subsystems with broken hierarchy support and whine if cgroups are nested for them

[Tejun Heo]

Hello, Michal.

On Thu, Sep 13, 2012 at 02:14:38PM +0200, Michal Hocko wrote:
> I would like to see use_hierarchy go away. The only concern I have is 
> to warn only if somebody is doing something wrong (aka flat
> hierarchies). Or better put it this way. Do not warn in cases which do
> not change if use_hierarchy is gone or default changes to 1.
> An example:
> root (use_hierarchy=0)
>  | \
>  |  A (use_hierarchy=0)
>  |
>  B (use_hierarachy=1)
>  |\
>  C D
> 
> is a perfectly sane configuration and I do not see any reason to fill
> logs with some scary warnings when A is created. There will be no
> semantical change in this setup When use_hierchy is gone.
> 
> So the only thing I am proposing here is to warn only if something
> should be fixed in the configuration in order to be prepared for fully
> hierarchical (and that is a second level of children from root with
> use_hierachy==0).
> 
> Does it make more sense now?

Ah, okay, so what you're saying is that we shouldn't warn if 0
.use_hierarchys don't make any behavior difference from when they're
all 1, right?  If so, I have no objection.  Will incorporate your
updated version.

Thanks.

-- 
tejun