On 09/15/2012 12:39 AM, Tejun Heo wrote:

Hello, again.

On Fri, Sep 14, 2012 at 12:49:50PM -0700, Tejun Heo wrote:

quoted

That said, if someone can think of a better solution, I'm all ears.
One thing that *has* to be maintained is that it should be able to tag
a resource in such way that its associated controllers are
identifiable regardless of which task is looking at it.

So, I thought about it more.  How about we do "consider / ignore this
node" instead of "(don't) nest beyond this level".  For example, let's
assume a tree like the following.

        R
     /  |  \
    A   B   C
   / \
  AA AB

If we want to differentiate between AA and AB, we'll have to consider
the whole tree with the previous sheme - A needs to nest, so R needs
to nest and we end up with the whole tree.  Instead, if we have honor
/ ignore this node.  We can set the honor bit on A, AA and AB and see
the tree as

        R
     /
    A
   / \
  AA AB

We still see the intermediate A node but can ignore the other
branches.  Implementation and concept-wise, it's fairly simple too.
For any given node and controller, you travel upwards until you meet a
node which has the controller enabled and that's the cgroup the
controller considers.

Thanks.

That is exactly what I proposed in our previous discussions around
memcg, with files like "available_controllers" , "current_controllers".
Name chosen to match what other subsystems already do.

if memcg is not in "available_controllers" for a node, it cannot be seen
by anyone bellow that level.