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    SubjectRe: [PATCH 5/6] Makes procs file writable to move all threads by tgid at once
    On Fri, Jul 24, 2009 at 10:23 AM, Matt Helsley<> wrote:
    > Well, I imagine holding tasklist_lock is worse than cgroup_mutex in some
    > ways since it's used even more widely. Makes sense not to use it here..

    Just to clarify - the new "procs" code doesn't use cgroup_mutex for
    its critical section, it uses a new cgroup_fork_mutex, which is only
    taken for write during cgroup_proc_attach() (after all setup has been
    done, to ensure that no new threads are created while we're updating
    all the existing threads). So in general there'll be zero contention
    on this lock - the cost will be the cache misses due to the rwlock
    bouncing between the different CPUs that are taking it in read mode.

    What happened to the big-reader lock concept from 2.4.x? That would be
    applicable here - minimizing the overhead on the critical path when
    the write operation is expected to be very rare.


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