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From: Ben Blum on 11 Aug 2010 01:50
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.

---
Documentation/cgroups/cgroups.txt | 13 -
include/linux/cgroup.h | 12
include/linux/init_task.h | 9
include/linux/sched.h | 35 ++
kernel/cgroup.c | 459 ++++++++++++++++++++++++++++++++++----
kernel/cgroup_freezer.c | 27 --
kernel/cpuset.c | 20 -
kernel/fork.c | 10
kernel/ns_cgroup.c | 27 +-
kernel/sched.c | 21 -
10 files changed, 526 insertions(+), 107 deletions(-)
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