Re: [ckrm-tech] [RFC] Resource Management - Infrastructure choices

[David Rientjes]

On Wed, 1 Nov 2006, Srivatsa Vaddagiri wrote:

> This would forces all tasks in container A to belong to the same mem/io ctlr 
> groups. What if that is not desired? How would we achieve something like
> this:
> 
> 	tasks (m) should belong to mem ctlr group D,
> 	tasks (n, o) should belong to mem ctlr group E
>   	tasks (m, n, o) should belong to i/o ctlr group G
> 

With the example you would need to place task m in one container called 
A_m and tasks n and o in another container called A_n,o.  Then join A_m to 
D, A_n,o to E, and both to G.

I agree that this doesn't appear to be very easy to setup by the sysadmin 
or any automated means.  But in terms of the kernel, each of these tasks 
would have a pointer back to its container and that container would point 
to its assigned resource controller.  So it's still a double dereference 
to access the controller from any task_struct.

So if we proposed a hierarchy of containers, we could have the following:

			----------A----------
			|         |         |
		   -----B-----	  m    -----C------
		   |         |         |
		   n    -----D-----    o
			|	  |
			p         q

So instead we make the requirement that only one container can be attached 
to any given controller.  So if container A is attached to a disk I/O 
controller, for example, then it includes all processes.  If D is attached 
to it instead, only p and q are affected by its constraints.

This would be possible by adding a field to the struct container that 
would point to its parent cpu, net, mem, etc. container or NULL if it is 
itself.

The difference:

	Single-level container hierarchy

		struct task_struct {
			...
			struct container *my_container;
		}
		struct container {
			...
			struct controller *my_cpu_controller;
			struct controller *my_mem_controller;
		}

	Multi-level container hierarchy

		struct task_struct {
			...
			struct container *my_container;
		}
		struct container {
			...
			/* Root containers, NULL if itself */
			struct container *my_cpu_root_container;
			struct container *my_mem_root_container;
			/* Controllers, NULL if has parent */
			struct controller *my_cpu_controller;
			struct controller *my_mem_controller;
		}

This eliminates the need to put a pointer to each resource controller 
within each task_struct.

> (this example breaks the required condition/assumption that a task belong to 
> exactly only one process container).
> 

Yes, and that was the requirement that the above example was based upon.

		David
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