[PATCH v5 0/3] cgroups: implement moving a threadgroup's threads atomically with cgroup.procs

[Ben Blum <bblum-OM76b2Iv3yLQjUSlxSEPGw@public.gmane.org>]

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(-)