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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 02:14:12AM -0700, Paul Menage wrote:
    > The general idea of passing consistent information to all *attach
    > methods seems good, but isn't it simpler to just fix up the various
    > method signatures?

    I think having separate ->attach() and ->attach_task() is inherently
    broken. Look at the memcg discussion I had in this thread for
    reference and as soon as we need to do something across the tasks
    being migrated, iteration-by-callback becomes very painful.
    e.g. let's say memcg wants to find the mm->owner and wants to print
    warning or fail if that doesn't work out. How would that be
    implemented if it's iterating by callback.

    > The whole point of having *attach() and *attach_task() was to minimize
    > the amount of boilerplate (in this case, iterating across a new
    > cgroup_taskset abstraction) in the subsystems, leaving that to the
    > cgroups framework.

    Yeah, I agree with making things easier for subsystems but I violently
    disagree that iteration-by-callback is helpful in any way. If
    control-loop style iterator is at all possible, it's almost always
    better to go that way.



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