feature: support Memory QoS for cgroups v2

cmd/kubelet/app/server.go

@@ -522,6 +522,11 @@ func run(ctx context.Context, s *options.KubeletServer, kubeDeps *kubelet.Depend
 		return err
 	}
 
+	// Warn if MemoryQoS enabled with cgroups v1
+	if utilfeature.DefaultFeatureGate.Enabled(features.MemoryQoS) &&
+		!isCgroup2UnifiedMode() {
+		klog.InfoS("Warning: MemoryQoS feature only works with cgroups v2 on Linux, but enabled with cgroups v1")
+	}
 	// Obtain Kubelet Lock File
 	if s.ExitOnLockContention && s.LockFilePath == "" {
 		return errors.New("cannot exit on lock file contention: no lock file specified")

cmd/kubelet/app/server_linux.go

@@ -19,6 +19,8 @@ package app
 import (
 	"k8s.io/klog/v2"
 	"k8s.io/utils/inotify"
+
+	libcontainercgroups "github.com/opencontainers/runc/libcontainer/cgroups"
 )
 
 func watchForLockfileContention(path string, done chan struct{}) error {
@@ -44,3 +46,7 @@ func watchForLockfileContention(path string, done chan struct{}) error {
 	}()
 	return nil
 }
+
+func isCgroup2UnifiedMode() bool {
+	return libcontainercgroups.IsCgroup2UnifiedMode()
+}

cmd/kubelet/app/server_unsupported.go

@@ -23,3 +23,7 @@ import "errors"
 func watchForLockfileContention(path string, done chan struct{}) error {
 	return errors.New("kubelet unsupported in this build")
 }
+
+func isCgroup2UnifiedMode() bool {
+	return false
+}