Adjusted docker stats memory output

Signed-off-by: Sergey Tryuber <Sergeant007@users.noreply.github.com>
Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

cli/command/container/stats_helpers.go

@@ -84,7 +84,7 @@ func collect(ctx context.Context, s *formatter.ContainerStats, cli client.APICli
 				v                      *types.StatsJSON
 				memPercent, cpuPercent float64
 				blkRead, blkWrite      uint64 // Only used on Linux
-				mem, memLimit, memPerc float64
+				mem, memLimit          float64
 				pidsStatsCurrent       uint64
 			)
 
@@ -101,18 +101,13 @@ func collect(ctx context.Context, s *formatter.ContainerStats, cli client.APICli
 			daemonOSType = response.OSType
 
 			if daemonOSType != "windows" {
-				// MemoryStats.Limit will never be 0 unless the container is not running and we haven't
-				// got any data from cgroup
-				if v.MemoryStats.Limit != 0 {
-					memPercent = float64(v.MemoryStats.Usage) / float64(v.MemoryStats.Limit) * 100.0
-				}
 				previousCPU = v.PreCPUStats.CPUUsage.TotalUsage
 				previousSystem = v.PreCPUStats.SystemUsage
 				cpuPercent = calculateCPUPercentUnix(previousCPU, previousSystem, v)
 				blkRead, blkWrite = calculateBlockIO(v.BlkioStats)
-				mem = float64(v.MemoryStats.Usage)
+				mem = calculateMemUsageUnixNoCache(v.MemoryStats)
 				memLimit = float64(v.MemoryStats.Limit)
-				memPerc = memPercent
+				memPercent = calculateMemPercentUnixNoCache(memLimit, mem)
 				pidsStatsCurrent = v.PidsStats.Current
 			} else {
 				cpuPercent = calculateCPUPercentWindows(v)
@@ -126,7 +121,7 @@ func collect(ctx context.Context, s *formatter.ContainerStats, cli client.APICli
 				ID:               v.ID,
 				CPUPercentage:    cpuPercent,
 				Memory:           mem,
-				MemoryPercentage: memPerc,
+				MemoryPercentage: memPercent,
 				MemoryLimit:      memLimit,
 				NetworkRx:        netRx,
 				NetworkTx:        netTx,
@@ -227,3 +222,18 @@ func calculateNetwork(network map[string]types.NetworkStats) (float64, float64)
 	}
 	return rx, tx
 }
+
+// calculateMemUsageUnixNoCache calculate memory usage of the container.
+// Page cache is intentionally excluded to avoid misinterpretation of the output.
+func calculateMemUsageUnixNoCache(mem types.MemoryStats) float64 {
+	return float64(mem.Usage - mem.Stats["cache"])
+}
+
+func calculateMemPercentUnixNoCache(limit float64, usedNoCache float64) float64 {
+	// MemoryStats.Limit will never be 0 unless the container is not running and we haven't
+	// got any data from cgroup
+	if limit != 0 {
+		return usedNoCache / limit * 100.0
+	}
+	return 0
+}

cli/command/container/stats_helpers_test.go

@@ -0,0 +1,42 @@
+package container
+
+import (
+	"github.com/docker/docker/api/types"
+	"testing"
+)
+
+func TestCalculateMemUsageUnixNoCache(t *testing.T) {
+	// Given
+	stats := types.MemoryStats{Usage: 500, Stats: map[string]uint64{"cache": 400}}
+
+	// When
+	result := calculateMemUsageUnixNoCache(stats)
+
+	// Then
+	if result != 100 {
+		t.Errorf("mem = %d, want 100", result)
+	}
+}
+
+func TestCalculateMemPercentUnixNoCache(t *testing.T) {
+	// Given
+	someLimit := float64(100.0)
+	noLimit := float64(0.0)
+	used := float64(70.0)
+
+	// When and Then
+	t.Run("Limit is set", func(t *testing.T) {
+		result := calculateMemPercentUnixNoCache(someLimit, used)
+		expected := float64(70.0)
+		if result != expected {
+			t.Errorf("percent = %f, want %f", result, expected)
+		}
+	})
+	t.Run("No limit, no cgroup data", func(t *testing.T) {
+		result := calculateMemPercentUnixNoCache(noLimit, used)
+		expected := float64(0.0)
+		if result != expected {
+			t.Errorf("percent = %f, want %f", result, expected)
+		}
+	})
+}