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

[Vivek Goyal]

On Tue, Oct 18, 2011 at 04:45:59PM -0400, Vivek Goyal wrote:
> Hi,

Oops, got old addresses of dhaval and bablir. Fixing it. Please reply 
to this mail instead of previous one.

Thanks
Vivek

> 
> 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