Changes coming for systemd and control groups

Lennart Poettering posted a message to the systemd-devel mailing list that outlines some changes coming. It refers to an earlier message that started describing differences coming in the kernel's control group (cgroup) implementation and their effects on systemd. Those cgroup changes were discussed in February 2012 and cgroup maintainer Tejun Heo decided to eventually drop multiple cgroup hierarchies in March 2012. The basic idea is that the single hierarchy will also have a single manager on the system and all changes to the cgroups will need to go through that manager. For systems that use it, systemd will become the manager of cgroups, so other tools that want to make changes will no longer follow the PaxControlGroups recommendations and will instead make D-Bus requests to systemd. Non-systemd systems will need to come up with their own manager and management interface once the cgroup changes are made in the kernel (for which the timeline is unclear). "In the long run there's only going to be a single kernel cgroup hierarchy, the per-controller hierarchies will go away. The single hierarchy will allow controllers to be individually enabled for each cgroup. The net effect is that the hierarchies the controllers see are not orthogonal anymore, they are always subtrees of the full single hierarchy."

