Fix workingset memory calculation.

Signed-off-by: Lantao Liu <lantaol@google.com>

pkg/server/container_stats_list_test.go

@@ -0,0 +1,55 @@
+/*
+Copyright 2018 The containerd 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 server
+
+import (
+	"testing"
+
+	"github.com/containerd/cgroups"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGetWorkingSet(t *testing.T) {
+	for desc, test := range map[string]struct {
+		memory   *cgroups.MemoryStat
+		expected uint64
+	}{
+		"nil memory usage": {
+			memory:   &cgroups.MemoryStat{},
+			expected: 0,
+		},
+		"memory usage higher than inactive_total_file": {
+			memory: &cgroups.MemoryStat{
+				TotalInactiveFile: 1000,
+				Usage:             &cgroups.MemoryEntry{Usage: 2000},
+			},
+			expected: 1000,
+		},
+		"memory usage lower than inactive_total_file": {
+			memory: &cgroups.MemoryStat{
+				TotalInactiveFile: 2000,
+				Usage:             &cgroups.MemoryEntry{Usage: 1000},
+			},
+			expected: 0,
+		},
+	} {
+		t.Run(desc, func(t *testing.T) {
+			got := getWorkingSet(test.memory)
+			assert.Equal(t, test.expected, got)
+		})
+	}
+}