[systemd-devel] Systemd and cgroup management (and libcgroup)

[Vivek Goyal]

Hi,

We have talked a lot of about libcgroup and systemd in the past and when I 
thought that debate is settled, here comes some more things to discuss.

Previously libcg was doing cgroup management and now sytemd is taken over
a lot of it.

- Creation of hierarchies. Taking control of hierarchies have taken away
  part of the cgconfig functionality.

- Providing automatic cgroups for users has taken away part of the
  functionality provided by cgroup pam plugin.

- Providing automatic cgroups for services has taken away the service
  management which in the past potentially could be done with the help
  of cgconfig.

Now systemd is managing services and users from cgroup point of view
which past init system never did and that was part of the reason to
have pam_cgroup plugin and cgconfig. Given the fact that new init
system has taken over a lot of cgroup management, few things come
to mind.

- Should systemd provide a way to change default cgroups of users as it
  provides for services.

- Should systemd provide a way to change default resources of cgroups of
  users as it provides for services.

- cgroup and associated resources now become properties of objects being
  managed by systemd (services and users). To me it will make sense
  to provide an API so that an application can call into those APIs
  and manage it. 

  Should systemd provide an API to manage cgroups and resources of cgroups
  of services and users it is managing.

  Lennart, I know you had said that editing the unit file is an API,
  but a real will API will help.

Should cgconfig equivalent functionality be owned by systemd
-----------------------------------------------------------
This is contentious one and I think there are two parts to it.

- Is cgconfig really needed. What are the use cases given the fact that
  systemd now takes care of setting up the system.

- If cgconfig is needed, then who should really manage it. systemd or
  libcg.

I am finding it hard to think of any good use cases of cgconfig now given
the fact systemd has taken over service and user management. What else is
left out. Everything is children of either user sessions of services
and they should manage their own children cgroups. Where's the need
of statically defining cgroups and resources and what will be launched
in those.

Even if there is, then it looks like systemd is better place to manage
it as it already is setting up the whole system and top level hierarchies.
Thanks to Jason for the suggestion.

Any thougths on above issues are appreciated.

Thanks
Vivek