cri: make swapping disabled with memory limit

OCI runtime spec defines memory.swap as 'limit of memory+Swap usage'
so setting them to equal should disable the swap. Also, this change
should make containerd behaviour same as other runtimes e.g
'cri-dockerd/dockershim' and won't be impacted when user turn on
'NodeSwap' (kubernetes/enhancements#2400) feature.

Signed-off-by: Qasim Sarfraz <qasimsarfraz@microsoft.com>

integration/container_update_resources_test.go

@@ -237,6 +237,13 @@ func TestUpdateContainerResources_MemoryLimit(t *testing.T) {
 	pauseImage := images.Get(images.Pause)
 	EnsureImageExists(t, pauseImage)
 
+	expectedSwapLimit := func(memoryLimit int64) *int64 {
+		if cgroups.Mode() == cgroups.Unified {
+			memoryLimit = 0
+		}
+		return &memoryLimit
+	}
+
 	t.Log("Create a container with memory limit")
 	cnConfig := ContainerConfig(
 		"container",
@@ -254,6 +261,7 @@ func TestUpdateContainerResources_MemoryLimit(t *testing.T) {
 	spec, err := container.Spec(context.Background())
 	require.NoError(t, err)
 	checkMemoryLimit(t, spec, 200*1024*1024)
+	checkMemorySwapLimit(t, spec, expectedSwapLimit(200*1024*1024))
 
 	t.Log("Update container memory limit after created")
 	err = runtimeService.UpdateContainerResources(cn, &runtime.LinuxContainerResources{
@@ -265,6 +273,7 @@ func TestUpdateContainerResources_MemoryLimit(t *testing.T) {
 	spec, err = container.Spec(context.Background())
 	require.NoError(t, err)
 	checkMemoryLimit(t, spec, 400*1024*1024)
+	checkMemorySwapLimit(t, spec, expectedSwapLimit(400*1024*1024))
 
 	t.Log("Start the container")
 	require.NoError(t, runtimeService.StartContainer(cn))
@@ -274,6 +283,8 @@ func TestUpdateContainerResources_MemoryLimit(t *testing.T) {
 	t.Log("Check memory limit in cgroup")
 	memLimit := getCgroupMemoryLimitForTask(t, task)
 	assert.Equal(t, uint64(400*1024*1024), memLimit)
+	swapLimit := getCgroupSwapLimitForTask(t, task)
+	assert.Equal(t, uint64(400*1024*1024), swapLimit)
 
 	t.Log("Update container memory limit after started")
 	err = runtimeService.UpdateContainerResources(cn, &runtime.LinuxContainerResources{
@@ -285,10 +296,14 @@ func TestUpdateContainerResources_MemoryLimit(t *testing.T) {
 	spec, err = container.Spec(context.Background())
 	require.NoError(t, err)
 	checkMemoryLimit(t, spec, 800*1024*1024)
+	checkMemorySwapLimit(t, spec, expectedSwapLimit(800*1024*1024))
 
 	t.Log("Check memory limit in cgroup")
 	memLimit = getCgroupMemoryLimitForTask(t, task)
 	assert.Equal(t, uint64(800*1024*1024), memLimit)
+	swapLimit = getCgroupSwapLimitForTask(t, task)
+	assert.Equal(t, uint64(800*1024*1024), swapLimit)
+
 }
 
 func TestUpdateContainerResources_StatusUpdated(t *testing.T) {

pkg/cri/opts/spec_linux.go

@@ -448,6 +448,10 @@ func WithResources(resources *runtime.LinuxContainerResources, tolerateMissingHu
 		}
 		if limit != 0 {
 			s.Linux.Resources.Memory.Limit = &limit
+			// swap/memory limit should be equal to prevent container from swapping by default
+			if swapLimit == 0 {
+				s.Linux.Resources.Memory.Swap = &limit
+			}
 		}
 		if swapLimit != 0 {
 			s.Linux.Resources.Memory.Swap = &swapLimit