[systemd-devel] Fedora 25, cgroups V2 and systemd roadmap

[Lennart Poettering]

On Mon, 10.10.16 14:31, Kevin Wilson (wkevils at gmail.com) wrote:

> Hello, systemd developers,
> So we have now 3 V2 cgroups controller in the kernel (pids, memory and io).
> The CPU controller as of now is not merged in and is available only in
> an out of tree git repo (due to some debate over
> it with kernel scheduler developers). Not sure that it will be merged
> in the next 2 months.
> 
> Fedora 25 is to be released in a month and a half, on 15 of November.
> https://fedoraproject.org/wiki/Releases/25/Schedule
> My questions are:
> what are the intentions regarding using cgroup v2 in systemd  in F25
> as the default instead of using cgroup V1?
> Is the absence of  the CPU controller is a reason for not having
> cgroup V2 as a default in F25 ? and if so, why ?

I'd like to switch this over sooner rather than later in Fedora, but I
figure we can't do that, unless relevant other upstreams can deal with
the new hierarchy too. I figure on Fedora, that'd be at least libvirt
and Docker that need to be updated for this.

I figure we should start turning this on in Rawhide, and see what
breaks, and then revert before the release.

Before we can tell Docker/libvirt to port their stuff over I figure we
also need one more addition in the systemd API for this: next to
Delegate=yes|no (which we already have) we probably need to add
DelegateController= taking a list of all controllers to
delegate. Right now we delegate all controllers, but I figure that
should be configurable, since turning on a controller might have
effects people don't expect (in particular for the cpu hierarchy).

Either way, we'd also have to post a Fedora feature page for this, to
make people aware, I figure.

Lennart

-- 
Lennart Poettering, Red Hat