cgroup.procs versus tasks (cgroups)

[Vlad Dogaru]

On Tue, Apr 02, 2013 at 05:54:56AM +0300, Kevin Wilson wrote:
> Hi?
> Any idea what is the difference  "cgroup.procs" entry and "tasks"
> entry of cgroup sysfs?
> both represent pid lists.
> I ran:
> cat /sys/fs/cgroup/cpuset/cgroup.procs
> and
> cat  /sys/fs/cgroup/cpuset/tasks
> and entries of cgroup.procs appear in tasks.
> 
> However there are many more tasks than cgroup.procs:
> 
> cat  /sys/fs/cgroup/cpuset/cgroup.procs | wc -l
> 153
> cat  /sys/fs/cgroup/cpuset/tasks | wc -l
> 383

The difference you are seeing is because there are some multithreaded
processes in your cpuset.  In the cgroup.procs file, each such process
apears only once (listed by its TGID).  In the tasks file, each thread
appears once (listed by its PID).

Check the pidlist_array_load function in kernel/cgroup.c.  procs is a
list of (unique) TGIDs, while tasks is a list of PIDs.

Hope this helps,
Vlad