Use tmpfs noswap if supported

use the tmpfs noswap option in order
to mount memory-backed volumes if it's supported.

Signed-off-by: Itamar Holder <iholder@redhat.com>

pkg/kubelet/util/swap/swap_util.go

@@ -0,0 +1,73 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package swap
+
+import (
+	"os"
+	sysruntime "runtime"
+	"sync"
+
+	"k8s.io/klog/v2"
+	"k8s.io/mount-utils"
+)
+
+var (
+	tmpfsNoswapOptionSupported        bool
+	tmpfsNoswapOptionAvailabilityOnce sync.Once
+)
+
+const TmpfsNoswapOption = "noswap"
+
+func IsTmpfsNoswapOptionSupported(mounter mount.Interface) bool {
+	isTmpfsNoswapOptionSupportedHelper := func() bool {
+		if sysruntime.GOOS == "windows" {
+			return false
+		}
+
+		mountDir, err := os.MkdirTemp("", "tmpfs-noswap-test-")
+		if err != nil {
+			klog.InfoS("error creating dir to test if tmpfs noswap is enabled. Assuming not supported", "mount path", mountDir, "error", err)
+			return false
+		}
+
+		defer func() {
+			err = os.RemoveAll(mountDir)
+			if err != nil {
+				klog.ErrorS(err, "error removing test tmpfs dir", "mount path", mountDir)
+			}
+		}()
+
+		err = mounter.MountSensitiveWithoutSystemd("tmpfs", mountDir, "tmpfs", []string{TmpfsNoswapOption}, nil)
+		if err != nil {
+			klog.InfoS("error mounting tmpfs with the noswap option. Assuming not supported", "error", err)
+			return false
+		}
+
+		err = mounter.Unmount(mountDir)
+		if err != nil {
+			klog.ErrorS(err, "error unmounting test tmpfs dir", "mount path", mountDir)
+		}
+
+		return true
+	}
+
+	tmpfsNoswapOptionAvailabilityOnce.Do(func() {
+		tmpfsNoswapOptionSupported = isTmpfsNoswapOptionSupportedHelper()
+	})
+
+	return tmpfsNoswapOptionSupported
+}

pkg/volume/emptydir/empty_dir.go

@@ -18,6 +18,7 @@ package emptydir
 
 import (
 	"fmt"
+	"k8s.io/kubernetes/pkg/kubelet/util/swap"
 	"os"
 	"path/filepath"
 
@@ -327,11 +328,7 @@ func (ed *emptyDir) setupTmpfs(dir string) error {
 		return nil
 	}
 
-	var options []string
+	options := ed.generateTmpfsMountOptions(swap.IsTmpfsNoswapOptionSupported(ed.mounter))
-	// Linux system default is 50% of capacity.
-	if ed.sizeLimit != nil && ed.sizeLimit.Value() > 0 {
-		options = []string{fmt.Sprintf("size=%d", ed.sizeLimit.Value())}
-	}
 
 	klog.V(3).Infof("pod %v: mounting tmpfs for volume %v", ed.pod.UID, ed.volName)
 	return ed.mounter.MountSensitiveWithoutSystemd("tmpfs", dir, "tmpfs", options, nil)
@@ -555,3 +552,16 @@ func getVolumeSource(spec *volume.Spec) (*v1.EmptyDirVolumeSource, bool) {
 
 	return volumeSource, readOnly
 }
+
+func (ed *emptyDir) generateTmpfsMountOptions(noswapSupported bool) (options []string) {
+	// Linux system default is 50% of capacity.
+	if ed.sizeLimit != nil && ed.sizeLimit.Value() > 0 {
+		options = append(options, fmt.Sprintf("size=%d", ed.sizeLimit.Value()))
+	}
+
+	if noswapSupported {
+		options = append(options, swap.TmpfsNoswapOption)
+	}
+
+	return options
+}