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SubjectRe: [PATCH 3/6] cgroup: introduce cgroup_taskset and use it in subsys->can_attach(), cancel_attach() and attach()
On Thu, Aug 25, 2011 at 07:38:18PM -0700, Matt Helsley wrote:
> On Fri, Aug 26, 2011 at 12:43:09AM +0200, Tejun Heo wrote:
> > Currently, there's no way to pass multiple tasks to cgroup_subsys
> > methods necessitating the need for separate per-process and per-task
> > methods. This patch introduces cgroup_taskset which can be used to
> > pass multiple tasks and their associated cgroups to cgroup_subsys
> > methods.
>
> This will be the third iterator-ish pattern in the cgroup code.
> It's not your fault but it does seem a bit much to have:
>
> 1) When we need to iterate over all tasks in the cgroup and
> don't mind holding the css set lock:
> void cgroup_iter_start(cgroup, iterator)
> task cgroup_iter_next(cgroup, iterator)
> void cgroup_iter_end(cgroup, iterator)
>
> 2) For subsystem methods when we're iterating over a subset of
> tasks that may or may not be in the cgroup (e.g. for can_attach)
> -- use cgroup_tasksets:
> task cgroup_taskset_first(tset)
> task cgroup_taskset_next(tset)
>
> 3) An iterator over all the tasks which doesn't hold the css set
> lock:
> struct cgroup_scanner {
> struct cgroup *cg;
> int (*test_task)(struct task_struct *p,
> struct cgroup_scanner *scan);
> void (*process_task)(struct task_struct *p,
> struct cgroup_scanner *scan);
> struct ptr_heap *heap;
> void *data;
> };
> This is only used in cpuset code so far. Are other cgroup
> patches planning on making use of it?
>
> Is there a sane way to merge all this?
>
> Perhaps we could drop the iterator interfaces in 1) and 2) and replace

Oops! I meant to suggest dropping interfaces 1) and 3).

Cheers,
-Matt


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