cgroupv2: fix setting MemorySwap

The resources.MemorySwap field from OCI is memory+swap, while cgroupv2
has a separate swap limit, so subtract memory from the limit (and make
sure values are set and sane).

Make sure to set MemorySwapMax for systemd, too. Since systemd does not
have MemorySwapMax for cgroupv1, it is only needed for v2 driver.

[v2: return -1 on any negative value, add unit test]
[v3: treat any negative value other than -1 as error]

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/fs2/memory.go

@@ -32,11 +32,16 @@ func numToStr(value int64) (ret string) {
 }
 
 func setMemory(dirPath string, cgroup *configs.Cgroup) error {
-	if val := numToStr(cgroup.Resources.MemorySwap); val != "" {
+	swap, err := cgroups.ConvertMemorySwapToCgroupV2Value(cgroup.Resources.MemorySwap, cgroup.Resources.Memory)
+	if err != nil {
+		return err
+	}
+	if val := numToStr(swap); val != "" {
 		if err := fscommon.WriteFile(dirPath, "memory.swap.max", val); err != nil {
 			return err
 		}
 	}
+
 	if val := numToStr(cgroup.Resources.Memory); val != "" {
 		if err := fscommon.WriteFile(dirPath, "memory.max", val); err != nil {
 			return err

libcontainer/cgroups/systemd/unified_hierarchy.go

@@ -84,6 +84,15 @@ func (m *UnifiedManager) Apply(pid int) error {
 			newProp("MemoryMax", uint64(c.Resources.Memory)))
 	}
 
+	swap, err := cgroups.ConvertMemorySwapToCgroupV2Value(c.Resources.MemorySwap, c.Resources.Memory)
+	if err != nil {
+		return err
+	}
+	if swap > 0 {
+		properties = append(properties,
+			newProp("MemorySwapMax", uint64(swap)))
+	}
+
 	if c.Resources.CpuWeight != 0 {
 		properties = append(properties,
 			newProp("CPUWeight", c.Resources.CpuWeight))

libcontainer/cgroups/utils.go

@@ -623,3 +623,25 @@ func ConvertCPUQuotaCPUPeriodToCgroupV2Value(quota int64, period uint64) string
 	}
 	return fmt.Sprintf("%d %d", quota, period)
 }
+
+// ConvertMemorySwapToCgroupV2Value converts MemorySwap value from OCI spec
+// for use by cgroup v2 drivers. A conversion is needed since Resources.MemorySwap
+// is defined as memory+swap combined, while in cgroup v2 swap is a separate value.
+func ConvertMemorySwapToCgroupV2Value(memorySwap, memory int64) (int64, error) {
+	if memorySwap == -1 || memorySwap == 0 {
+		// -1 is "max", 0 is "unset", so treat as is
+		return memorySwap, nil
+	}
+	// sanity checks
+	if memory == 0 || memory == -1 {
+		return 0, errors.New("unable to set swap limit without memory limit")
+	}
+	if memory < 0 {
+		return 0, fmt.Errorf("invalid memory value: %d", memory)
+	}
+	if memorySwap < memory {
+		return 0, errors.New("memory+swap limit should be > memory limit")
+	}
+
+	return memorySwap - memory, nil
+}

libcontainer/cgroups/utils_test.go

@@ -530,3 +530,84 @@ func TestConvertCPUQuotaCPUPeriodToCgroupV2Value(t *testing.T) {
 		}
 	}
 }
+
+func TestConvertMemorySwapToCgroupV2Value(t *testing.T) {
+	cases := []struct {
+		memswap, memory int64
+		expected        int64
+		expErr          bool
+	}{
+		{
+			memswap:  0,
+			memory:   0,
+			expected: 0,
+		},
+		{
+			memswap:  -1,
+			memory:   0,
+			expected: -1,
+		},
+		{
+			memswap:  -1,
+			memory:   -1,
+			expected: -1,
+		},
+		{
+			memswap: -2,
+			memory:  0,
+			expErr:  true,
+		},
+		{
+			memswap:  -1,
+			memory:   1000,
+			expected: -1,
+		},
+		{
+			memswap:  1000,
+			memory:   1000,
+			expected: 0,
+		},
+		{
+			memswap:  500,
+			memory:   200,
+			expected: 300,
+		},
+		{
+			memswap: 300,
+			memory:  400,
+			expErr:  true,
+		},
+		{
+			memswap: 300,
+			memory:  0,
+			expErr:  true,
+		},
+		{
+			memswap: 300,
+			memory:  -300,
+			expErr:  true,
+		},
+		{
+			memswap: 300,
+			memory:  -1,
+			expErr:  true,
+		},
+	}
+
+	for _, c := range cases {
+		swap, err := ConvertMemorySwapToCgroupV2Value(c.memswap, c.memory)
+		if c.expErr {
+			if err == nil {
+				t.Errorf("memswap: %d, memory %d, expected error, got %d, nil", c.memswap, c.memory, swap)
+			}
+			// no more checks
+			continue
+		}
+		if err != nil {
+			t.Errorf("memswap: %d, memory %d, expected success, got error %s", c.memswap, c.memory, err)
+		}
+		if swap != c.expected {
+			t.Errorf("memswap: %d, memory %d, expected %d, got %d", c.memswap, c.memory, c.expected, swap)
+		}
+	}
+}