In cgroups v2 we need to handle threads and processes differently.
If you need to move a process you need to write its pid into
cgrou.procs file and it will move the process with all its threads
as well. The whole process will be moved if you use tid of any thread.
In order to move only threads at first we need to create threaded group
and after that we can write the relevant thread tids into cgroup.threads
file. Threads can be moved only into cgroups that are children of
cgroup of its process.
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
When creating cgroup hierarchy we need to enable controllers in the
parent cgroup in order to be usable. That means writing "+{controller}"
into cgroup.subtree_control file. We can enable only controllers that
are enabled for parent cgroup, that means we need to do that for the
whole cgroup tree.
Cgroups for threads needs to be handled differently in cgroup v2. There
are two types of controllers:
- domain controllers: these cannot be enabled for threads
- threaded controllers: these can be enabled for threads
In addition there are multiple types of cgroups:
- domain: normal cgroup
- domain threaded: a domain cgroup that serves as root for threaded
cgroups
- domain invalid: invalid cgroup, can be changed into threaded, this
is the default state if you create subgroup inside
domain threaded group or threaded group
- threaded: threaded cgroup which can have domain threaded or
threaded as parent group
In order to create threaded cgroup it's sufficient to write "threaded"
into cgroup.type file, it will automatically make parent cgroup
"domain threaded" if it was only "domain". In case the parent cgroup
is already "domain threaded" or "threaded" it will modify only the type
of current cgroup. After that we can enable threaded controllers.
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Cgroup v2 has only single mount point for all controllers. The list
of controllers is stored in cgroup.controllers file, name of controllers
are separated by space.
In cgroup v2 there is no cpuacct controller, the cpu.stat file always
exists with usage stats.
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
If the placement was copied from parent or set to absolute path
there is nothing to do, otherwise set the placement based on
process placement from /proc/self/cgroup or /proc/{pid}/cgroup.
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
When reconnecting to a domain we are validating the cgroup name.
In case of cgroup v2 we need to validate only the new format for host
without systemd '{machinename}.libvirt-{drivername}' or scope name
generated by systemd.
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
We cannot detect only mount points to figure out whether cgroup v2
is available because systemd uses cgroup v2 for process tracking and
all controllers are mounted as cgroup v1 controllers.
To make sure that this is no the situation we need to check
'cgroup.controllers' file if it's not empty to make sure that cgroup
v2 is not mounted only for process tracking.
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Place cgroup v2 backend type before cgroup v1 to make it obvious
that cgroup v2 is preferred implementation.
Following patches will introduce support for hybrid configuration
which will allow us to use both at the same time, but we should
prefer cgroup v2 regardless.
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
