Handle memory swappiness as a pointer to handle default/unset case

This prior fix to set "-1" explicitly was lost, and it is simpler to use
the same pointer type from the OCI spec to handle nil pointer == -1 ==
unset case.

Also, as a nearly humorous aside, there was a test for MemorySwappiness
that was actually setting Memory, and it was passing because of this
bug (as it was always setting everyone's MemorySwappiness to zero!)

Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)

libcontainer/cgroups/fs/memory.go

@@ -86,14 +86,14 @@ func (s *MemoryGroup) Set(path string, cgroup *configs.Cgroup) error {
 			return err
 		}
 	}
-	if cgroup.Resources.MemorySwappiness >= 0 && cgroup.Resources.MemorySwappiness <= 100 {
-		if err := writeFile(path, "memory.swappiness", strconv.FormatInt(cgroup.Resources.MemorySwappiness, 10)); err != nil {
+	if cgroup.Resources.MemorySwappiness == nil || int64(*cgroup.Resources.MemorySwappiness) == -1 {
+		return nil
+	} else if int64(*cgroup.Resources.MemorySwappiness) >= 0 && int64(*cgroup.Resources.MemorySwappiness) <= 100 {
+		if err := writeFile(path, "memory.swappiness", strconv.FormatInt(*cgroup.Resources.MemorySwappiness, 10)); err != nil {
 			return err
 		}
-	} else if cgroup.Resources.MemorySwappiness == -1 {
-		return nil
 	} else {
-		return fmt.Errorf("invalid value:%d. valid memory swappiness range is 0-100", cgroup.Resources.MemorySwappiness)
+		return fmt.Errorf("invalid value:%d. valid memory swappiness range is 0-100", int64(*cgroup.Resources.MemorySwappiness))
 	}
 
 	return nil
@@ -149,7 +149,7 @@ func memoryAssigned(cgroup *configs.Cgroup) bool {
 		cgroup.Resources.MemorySwap > 0 ||
 		cgroup.Resources.KernelMemory > 0 ||
 		cgroup.Resources.OomKillDisable ||
-		cgroup.Resources.MemorySwappiness != -1
+		(cgroup.Resources.MemorySwappiness != nil && *cgroup.Resources.MemorySwappiness != -1)
 }
 
 func getMemoryData(path, name string) (cgroups.MemoryData, error) {

libcontainer/cgroups/fs/memory_test.go

@@ -119,15 +119,15 @@ func TestMemorySetMemorySwappinessDefault(t *testing.T) {
 	defer helper.cleanup()
 
 	const (
-		swappinessBefore = 60 //deafult is 60
-		swappinessAfter  = 0
+		swappinessBefore = 60 //default is 60
+		swappinessAfter  = int64(0)
 	)
 
 	helper.writeFileContents(map[string]string{
 		"memory.swappiness": strconv.Itoa(swappinessBefore),
 	})
 
-	helper.CgroupData.config.Resources.Memory = swappinessAfter
+	helper.CgroupData.config.Resources.MemorySwappiness = &swappinessAfter
 	memory := &MemoryGroup{}
 	if err := memory.Set(helper.CgroupPath, helper.CgroupData.config); err != nil {
 		t.Fatal(err)
@@ -138,7 +138,7 @@ func TestMemorySetMemorySwappinessDefault(t *testing.T) {
 		t.Fatalf("Failed to parse memory.swappiness - %s", err)
 	}
 	if value != swappinessAfter {
-		t.Fatal("Got the wrong value, set memory.swappiness failed.")
+		t.Fatalf("Got the wrong value (%d), set memory.swappiness = %d failed.", value, swappinessAfter)
 	}
 }
 

libcontainer/configs/cgroup_unix.go

@@ -111,7 +111,7 @@ type Resources struct {
 	OomKillDisable bool `json:"oom_kill_disable"`
 
 	// Tuning swappiness behaviour per cgroup
-	MemorySwappiness int64 `json:"memory_swappiness"`
+	MemorySwappiness *int64 `json:"memory_swappiness"`
 
 	// Set priority of network traffic for container
 	NetPrioIfpriomap []*IfPrioMap `json:"net_prio_ifpriomap"`

libcontainer/integration/template_test.go

@@ -48,7 +48,7 @@ func newTemplateConfig(rootfs string) *configs.Config {
 		Cgroups: &configs.Cgroup{
 			Path: "integration/test",
 			Resources: &configs.Resources{
-				MemorySwappiness: -1,
+				MemorySwappiness: nil,
 				AllowAllDevices:  false,
 				AllowedDevices:   configs.DefaultAllowedDevices,
 			},

spec.go

@@ -398,7 +398,8 @@ func createCgroupConfig(name string, spec *specs.LinuxSpec) (*configs.Cgroup, er
 			c.Resources.KernelMemory = int64(*r.Memory.Kernel)
 		}
 		if r.Memory.Swappiness != nil {
-			c.Resources.MemorySwappiness = int64(*r.Memory.Swappiness)
+			swappiness := int64(*r.Memory.Swappiness)
+			c.Resources.MemorySwappiness = &swappiness
 		}
 	}
 	if r.CPU != nil {