[systemd-devel] [ANNOUNCE] systemd 190

[Eelco Dolstra]

Hi,

On 20/09/12 16:39, Lennart Poettering wrote:

>         * We will now mount the cgroup controllers cpu, cpuacct,
>           cpuset and the controllers net_cls, net_prio together by
>           default.

Joining the cpuset controller with cpu/cpuacct caused problems on my system
(NixOS Linux): services, in particular those using "Type=forking", would
randomly fail to start.  It turns out that this is because systemd uses the cpu
hierarchy to determine if a service has any running processes left, but the
addition of cpuset causes adding tasks to control groups to fail with ENOSPC:

open("/sys/fs/cgroup/cpu/system/nscd.service/control/tasks",
O_WRONLY|O_CREAT|O_TRUNC|O_CLOEXEC, 0666) = 30
write(30, "7210\n", 5)                  = -1 ENOSPC (No space left on device)

Because "tasks" remains empty, systemd concludes that the service has no
processes left and kills it.  (For the killing it uses
/sys/fs/cgroup/systemd/system/<service>/cgroup.procs, which *does* have the
correct contents.)

The ENOSPC is because the attributes /sys/fs/cgroup/cpu/.../cpuset.{mems,cpus}
are not set in the per-service cgroups, as required by the cpuset controller.
Apparently setting /sys/fs/cgroup/cpu/cgroup.clone_children to 1 should cause
cpuset.{mems,cpus} to be inherited from the top-level cgroup, but as far as I
can tell, systemd doesn't set clone_children anywhere.  What is the right way to
deal with this?

Thanks,

Eelco.

-- 
Eelco Dolstra | LogicBlox, Inc. | http://nixos.org/~eelco/