[systemd-devel] Avoiding creating systemd memory and blkio controllers under /sys/fs/cgroup/memory and /sys/fs/cgroup/blkio.

[Lennart Poettering]

On Fri, 15.01.16 22:17, Kevin Wilson (wkevils at gmail.com) wrote:

> Hi everyone,
> 
> I had a Fedora 20 Machine (x86_64) on which I installed the
> latest 4.4 kernel released this week (I had built it from source). It
> had systemd  208.
> 
> I wanted to test cgroup v2 (not in relation to systemd). In order to
> be able to activate
> cgoupv2 memory and cgroup controllers, the cgroup v1 controllers must
> be disabled.
> 
> When I unmounted /sys/fs/cgroup/memory and /sys/fs/cgroup/blkio and mounted
> cgroup v2 on /testv2, cat /testv2/cgroup.controllers showed
> "memeory" and "io", and everything was fine.
> 
> Then I installed Fedora 22 on this machine, and it has systemd 219.
> When I tried this
> same sequence, of unmounting /sys/fs/cgroup/memory and /sys/fs/cgroup/blkio and
> mounting cgroup v2 on /testv2, cat /testv2/cgroup.controllers showed nothing.
> 
> Trying to add disabling cgroup memory controller, by adding
> cgroup_disable=memory,
> to the kernel command line caused the system to hang in boot (which is
> what I expected,
> but tried anyway...)
> 
> Trying to solve the problem, I came to the conclusion that this is
> probably because
> there are processes in the memory and blkio groups which are held by
> systemd in F22, and  which are not held in F20.
> 
> On the F22, when I look under /sys/fs/cgouop/memory, I see
> 
> /sys/fs/cgroup/memory/user.slice/
> /sys/fs/cgroup/memory/user.slice/user-0.slice/
> /sys/fs/cgroup/memory/user.slice/user-0.slice/session-10.scope
> /sys/fs/cgroup/memory/user.slice/user-0.slice/session-2.scope
> /sys/fs/cgroup/memory/user.slice/user-0.slice/session-9.scope
> and more
> 
> And there are pids in many of the tasks entries under this directories.
> 
> And for the blkio:
>  /sys/fs/cgroup/blkio/system.slice/
>  /sys/fs/cgroup/blkio/user.slice/
>  /sys/fs/cgroup/blkio/user.slice/user-0.slice/
>  /sys/fs/cgroup/blkio/user.slice/user-0.slice/session-10.scope/
>  /sys/fs/cgroup/blkio/user.slice/user-0.slice/session-2.scope/
> /sys/fs/cgroup/blkio/user.slice/user-0.slice/session-9.scope/
> and more.
> 
> And here again there are pids in many of the tasks entries under this
> directories.
> 
> On the Fedora 20 machine, these entries do not exist, namely there are no
> systemd entries under both  /sys/fs/cgroup/memory/ and
> /sys/fs/cgroup/blkio.
> 
> Is there a way to disable creating these entries by systemd ?

Upgrade your systemd version. Old versions will add all controllers to
"delegation" scopes or services. Newer version don't do that.

Lennart

-- 
Lennart Poettering, Red Hat