merge issue-10491, but only stats_helpers.go file

plugins/inputs/docker/docker_test.go

@@ -104,7 +104,7 @@ var baseClient = MockClient{
 	},
 	CloseF: func() error {
 		return nil
-	}
+	},
 }
 
 func newClient(host string, tlsConfig *tls.Config) (Client, error) {

plugins/inputs/docker/stats_helpers.go

@@ -41,8 +41,27 @@ func calculateCPUPercentWindows(v *types.StatsJSON) float64 {
 
 // CalculateMemUsageUnixNoCache calculate memory usage of the container.
 // Page cache is intentionally excluded to avoid misinterpretation of the output.
+//
+// On Docker 19.03 and older, the result is `mem.Usage - mem.Stats["cache"]`.
+// On new docker with cgroup v1 host, the result is `mem.Usage - mem.Stats["total_inactive_file"]`.
+// On new docker with cgroup v2 host, the result is `mem.Usage - mem.Stats["inactive_file"]`.
+//
+// This definition is designed to be consistent with past values and the latest docker CLI
+// * https://github.com/docker/cli/blob/6e2838e18645e06f3e4b6c5143898ccc44063e3b/cli/command/container/stats_helpers.go#L239
 func CalculateMemUsageUnixNoCache(mem types.MemoryStats) float64 {
-	return float64(mem.Usage - mem.Stats["cache"])
+	// Docker 19.03 and older
+	if v, isOldDocker := mem.Stats["cache"]; isOldDocker && v < mem.Usage {
+		return float64(mem.Usage - v)
+	}
+	// cgroup v1
+	if v, isCgroup1 := mem.Stats["total_inactive_file"]; isCgroup1 && v < mem.Usage {
+		return float64(mem.Usage - v)
+	}
+	// cgroup v2
+	if v := mem.Stats["inactive_file"]; v < mem.Usage {
+		return float64(mem.Usage - v)
+	}
+	return float64(mem.Usage)
 }
 
 func CalculateMemPercentUnixNoCache(limit float64, usedNoCache float64) float64 {