live objects metric

src/runtime/metrics.go

@@ -247,6 +247,13 @@ func initMetrics() {
 				out.scalar = in.sysStats.heapGoal
 			},
 		},
+		"/gc/heap/live:bytes": {
+			deps: makeStatDepSet(heapStatsDep),
+			compute: func(in *statAggregate, out *metricValue) {
+				out.kind = metricKindUint64
+				out.scalar = gcController.heapMarked
+			},
+		},
 		"/gc/heap/objects:objects": {
 			deps: makeStatDepSet(heapStatsDep),
 			compute: func(in *statAggregate, out *metricValue) {

src/runtime/metrics/description.go

@@ -241,6 +241,11 @@ var allDesc = []Description{
 		Description: "Heap size target for the end of the GC cycle.",
 		Kind:        KindUint64,
 	},
+	{
+		Name:        "/gc/heap/live:bytes",
+		Description: "Heap memory occupied by live objects that were marked by the previous GC.",
+		Kind:        KindUint64,
+	},
 	{
 		Name:        "/gc/heap/objects:objects",
 		Description: "Number of objects, live or unswept, occupying heap memory.",

src/runtime/metrics/doc.go

@@ -176,6 +176,9 @@ Below is the full list of supported metrics, ordered lexicographically.
 	/gc/heap/goal:bytes
 		Heap size target for the end of the GC cycle.
 
+	/gc/heap/live:bytes
+		Heap memory occupied by live objects that were marked by the previous GC.
+
 	/gc/heap/objects:objects
 		Number of objects, live or unswept, occupying heap memory.
 

src/runtime/metrics_test.go

@@ -183,6 +183,7 @@ func TestReadMetricsConsistency(t *testing.T) {
 		allocs, frees           uint64
 		allocdBytes, freedBytes uint64
 		total, totalBytes       uint64
+		liveBytes               uint64
 	}
 	var gc struct {
 		numGC  uint64
@@ -248,6 +249,8 @@ func TestReadMetricsConsistency(t *testing.T) {
 			totalVirtual.got = samples[i].Value.Uint64()
 		case "/memory/classes/heap/objects:bytes":
 			objects.totalBytes = samples[i].Value.Uint64()
+		case "/gc/heap/live:bytes":
+			objects.liveBytes = samples[i].Value.Uint64()
 		case "/gc/heap/objects:objects":
 			objects.total = samples[i].Value.Uint64()
 		case "/gc/heap/allocs:bytes":
@@ -313,6 +316,9 @@ func TestReadMetricsConsistency(t *testing.T) {
 	if got, want := objects.allocs-objects.frees, objects.total; got != want {
 		t.Errorf("mismatch between object alloc/free tallies and total: got %d, want %d", got, want)
 	}
+	if objects.liveBytes > objects.totalBytes {
+		t.Errorf("liveBytes bytes: %d > totalBytes: %d", objects.liveBytes, objects.totalBytes)
+	}
 	if got, want := objects.allocdBytes-objects.freedBytes, objects.totalBytes; got != want {
 		t.Errorf("mismatch between object alloc/free tallies and total: got %d, want %d", got, want)
 	}