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You can enable Linux control group version 2 (cgroup v2) in your cluster by editing the node.config object. Enabling cgroup v2 in OKD disables all cgroups version 1 controllers and hierarchies in your cluster. cgroup v1 is enabled by default.

cgroup v2 is the next version of the Linux cgroup API. cgroup v2 offers several improvements over cgroup v1, including a unified hierarchy, safer sub-tree delegation, new features such as Pressure Stall Information, and enhanced resource management and isolation.

OKD cgroups version 2 support is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview/.

Configuring Linux cgroup v2

You enable cgroup v2 by editing the node.config object.

Prerequisites
  • You have a running OKD cluster that uses version 4.12 or later.

  • You are logged in to the cluster as a user with administrative privileges.

  • You have enabled the TechPreviewNoUpgrade feature set by using the feature gates.

Procedure
  1. Enable cgroup v2 on nodes:

    1. Edit the node.config object:

      $ oc edit nodes.config/cluster
    2. Add spec.cgroupMode: "v2":

      Example node.config object
      apiVersion: config.openshift.io/v1
      kind: Node
      metadata:
        annotations:
          include.release.openshift.io/ibm-cloud-managed: "true"
          include.release.openshift.io/self-managed-high-availability: "true"
          include.release.openshift.io/single-node-developer: "true"
          release.openshift.io/create-only: "true"
        creationTimestamp: "2022-07-08T16:02:51Z"
        generation: 1
        name: cluster
        ownerReferences:
        - apiVersion: config.openshift.io/v1
          kind: ClusterVersion
          name: version
          uid: 36282574-bf9f-409e-a6cd-3032939293eb
        resourceVersion: "1865"
        uid: 0c0f7a4c-4307-4187-b591-6155695ac85b
      spec:
        cgroupMode: "v2" (1)
      ...
      1 Enables cgroup v2.
Verification
  1. Check the machine configs to see that the new machine configs were added:

    $ oc get mc
    Example output
    NAME                                               GENERATEDBYCONTROLLER                      IGNITIONVERSION   AGE
    00-master                                          52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    00-worker                                          52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-master-container-runtime                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-master-kubelet                                  52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-worker-container-runtime                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-worker-kubelet                                  52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    97-master-generated-kubelet                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0              3m (1)
    99-worker-generated-kubelet                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0              3m
    99-master-generated-registries                     52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    99-master-ssh                                                                                 3.2.0             40m
    99-worker-generated-registries                     52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    99-worker-ssh                                                                                 3.2.0             40m
    rendered-master-23e785de7587df95a4b517e0647e5ab7   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    rendered-worker-5d596d9293ca3ea80c896a1191735bb1   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    worker-enable-cgroups-v2                                                                      3.2.0             10s
    1 New machine configs are created, as expected.
  2. Check that the new kernelArguments were added to the new machine configs:

    $ oc describe mc <name>
    Example output
    apiVersion: machineconfiguration.openshift.io/v1
    kind: MachineConfig
    metadata:
      labels:
        machineconfiguration.openshift.io/role: worker
      name: 05-worker-kernelarg-selinuxpermissive
    spec:
      kernelArguments:
      - systemd_unified_cgroup_hierarchy=1 (1)
      - cgroup_no_vi="all" (2)
      - psi=1 (3)
    
    1 Enables cgroup v2 in systemd.
    2 Disables cgroups v1.
    3 Enables the Linux Pressure Stall Information (PSI) feature.
  3. Check the nodes to see that scheduling on the nodes is disabled. This indicates that the change is being applied:

    $ oc get nodes
    Example output
    NAME                                       STATUS                     ROLES    AGE   VERSION
    ci-ln-fm1qnwt-72292-99kt6-master-0         Ready                      master   58m   v1.24.0
    ci-ln-fm1qnwt-72292-99kt6-master-1         Ready                      master   58m   v1.24.0
    ci-ln-fm1qnwt-72292-99kt6-master-2         Ready                      master   58m   v1.24.0
    ci-ln-fm1qnwt-72292-99kt6-worker-a-h5gt4   Ready,SchedulingDisabled   worker   48m   v1.24.0
    ci-ln-fm1qnwt-72292-99kt6-worker-b-7vtmd   Ready                      worker   48m   v1.24.0
    ci-ln-fm1qnwt-72292-99kt6-worker-c-rhzkv   Ready                      worker   48m   v1.24.0
  4. After a node returns to the Ready state, start a debug session for that node:

    $ oc debug node/<node_name>
  5. Set /host as the root directory within the debug shell:

    sh-4.4# chroot /host
  6. Check that the sys/fs/cgroup/cgroup2fs file is present on your nodes. This file is created by cgroup v2:

    $ stat -c %T -f /sys/fs/cgroup
    Example output
    cgroup2fs