[systemd-devel] How does hybrid cgroup setup work?

[Umut Tezduyar Lindskog]

On Wed, Nov 8, 2017 at 9:25 PM, Lennart Poettering
<lennart at poettering.net> wrote:
> On Sa, 28.10.17 22:01, Umut Tezduyar Lindskog (umut at tezduyar.com) wrote:
>
>> Hello,
>>
>> I am trying to have cpu controller on v1 and memory controller on
>> unified but it is not working the way I am expecting. When I enable
>> CONFIG_MEMCG, cgroup is popping up in /proc/cgroups and
>> mount_cgroup_controllers() is mounting it very early. Once it is
>> mounted in v1, it becomes unavailable in v2.
>>
>> Did I misunderstand how hybrid works?
>
> hybrid means that v2 is used only for tracking services (which is a
> good thing, since it provides safe notification of when a cgroup
> exits), but not for any of the controllers. That means hybrid mode is
> mostly compatible with pure v1, except that there's yet another
> hierarchy (the v2 one) and systemd uses it for its own purposes.

Is there a technical reason why we cannot have a broader hybrid like
some controllers from v1 and some from v2?

We would like to keep using cpu v1 until cpu v2 is accepted but
meanwhile take advantage of improvements on memory v2.

UMUT

>
> Lennart
>
> --
> Lennart Poettering, Red Hat