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    Subject[PATCH v6 0/3] cgroups: implement moving a threadgroup's threads atomically with cgroup.procs
    On Wed, Aug 11, 2010 at 01:46:04AM -0400, Ben Blum wrote:
    > On Fri, Jul 30, 2010 at 07:56:49PM -0400, Ben Blum wrote:
    > > This patch series is a revision of http://lkml.org/lkml/2010/6/25/11 .
    > >
    > > This patch series implements a write function for the 'cgroup.procs'
    > > per-cgroup file, which enables atomic movement of multithreaded
    > > applications between cgroups. Writing the thread-ID of any thread in a
    > > threadgroup to a cgroup's procs file causes all threads in the group to
    > > be moved to that cgroup safely with respect to threads forking/exiting.
    > > (Possible usage scenario: If running a multithreaded build system that
    > > sucks up system resources, this lets you restrict it all at once into a
    > > new cgroup to keep it under control.)
    > >
    > > Example: Suppose pid 31337 clones new threads 31338 and 31339.
    > >
    > > # cat /dev/cgroup/tasks
    > > ...
    > > 31337
    > > 31338
    > > 31339
    > > # mkdir /dev/cgroup/foo
    > > # echo 31337 > /dev/cgroup/foo/cgroup.procs
    > > # cat /dev/cgroup/foo/tasks
    > > 31337
    > > 31338
    > > 31339
    > >
    > > A new lock, called threadgroup_fork_lock and living in signal_struct, is
    > > introduced to ensure atomicity when moving threads between cgroups. It's
    > > taken for writing during the operation, and taking for reading in fork()
    > > around the calls to cgroup_fork() and cgroup_post_fork(). I put calls to
    > > down_read/up_read directly in copy_process(), since new inline functions
    > > seemed like overkill.
    > >
    > > -- Ben
    > >
    > > ---
    > > Documentation/cgroups/cgroups.txt | 13 -
    > > include/linux/init_task.h | 9
    > > include/linux/sched.h | 10
    > > kernel/cgroup.c | 426 +++++++++++++++++++++++++++++++++-----
    > > kernel/cgroup_freezer.c | 4
    > > kernel/cpuset.c | 4
    > > kernel/fork.c | 16 +
    > > kernel/ns_cgroup.c | 4
    > > kernel/sched.c | 4
    > > 9 files changed, 440 insertions(+), 50 deletions(-)
    >
    > Here's an updated patchset. I've added an extra patch to implement the
    > callback scheme Paul suggested (note how there are twice as many deleted
    > lines of code as before :) ), and also moved the up_read/down_read calls
    > to static inline functions in sched.h near the other threadgroup-related
    > calls.

    One more go at this. I've refreshed the patches for some conflicts in
    cgroup_freezer.c, by adding an extra argument to the per_thread() call,
    "need_rcu", which makes the function take rcu_read_lock even around the
    single-task case (like freezer now requires). So no semantics have been
    changed.

    I also poked around at some attach() calls which also iterate over the
    threadgroup (blkiocg_attach, cpuset_attach, cpu_cgroup_attach). I was
    borderline about making another function, cgroup_attach_per_thread(),
    but decided against.

    There is a big issue in cpuset_attach, as explained in this email:
    http://www.spinics.net/lists/linux-containers/msg22223.html
    but the actual code/diffs for this patchset are independent of that
    getting fixed, so I'm putting this up for consideration now.

    -- Ben

    ---
    Documentation/cgroups/cgroups.txt | 13 -
    block/blk-cgroup.c | 31 ++
    include/linux/cgroup.h | 14 +
    include/linux/init_task.h | 9
    include/linux/sched.h | 35 ++
    kernel/cgroup.c | 469 ++++++++++++++++++++++++++++++++++----
    kernel/cgroup_freezer.c | 33 +-
    kernel/cpuset.c | 30 --
    kernel/fork.c | 10
    kernel/ns_cgroup.c | 25 --
    kernel/sched.c | 24 -
    11 files changed, 565 insertions(+), 128 deletions(-)


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