[Devel] [PATCH v6 0/3] cgroups: implement moving a threadgroup's threads atomically with cgroup.procs

[Ben Blum]

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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