Can not remove the subdirectory in cgroup pseudo-filesystem

[Li Zefan]

anqin wrote:
>> Yes you have to initialize some cpuset files first.  Otherwise
>> the tasks have no access to any memory or cpus.
>>
> 
> Oh... thank you for reminding. Previously, I run my tests in
> a experimental kernel, it seems someone has set the
> parameters.
> 
> 
> BTW, is it possible currently to combine two tasks into
> one cgroup? for instance, I have run two bashes (bash_A and

I recomend you to read Documentation/cgroups/cgroups.txt to know
cgroup better. Cgroup is used to aggregate/partition sets of tasks,
so of course you can put more than 1 task into a cgroup.

> bash_B). Now, in bash_A, I created a cgroup in procfs:
> 
> # mount -t cgroup cgroup /mnt/cgrp

mount cgroupfs with all cgroup subsystems is not so sane IMO.

> # cd /mnt/cgrp
> # mkdir test
> # echo $$ > test/tasks
> 
> Then, I would like to add bash_B in this task group but
> fail:
> 
> # echo #(PID_OF_bash_B) >  test/tasks
> -bash: echo: write error: Operation not permitted
> 

That's because ns_cgroup is binded in this cgroup hierarchy, and
it's ns_cgroup that prevents the task attaching, but a patch in
-mm tree relaxes this check, and you won't see this restriction
when using ns_cgroup.

> It seems the cgroup can not couple two irrelevant
> task together, right?
> 
> 
> Best,
> 
> Anqin