runtime/metrics: add additional allocation metrics

This change adds four additional metrics to the runtime/metrics package
to fill in a few gaps with runtime.MemStats that were overlooked. The
biggest one is TotalAlloc, which is impossible to find with the
runtime/metrics package, but also add a few others for convenience and
clarity. For instance, the total number of objects allocated and freed
are technically available via allocs-by-size and frees-by-size, but it's
onerous to get them (one needs to sum the sample counts in the
histograms).

The four additional metrics are:
- /gc/heap/allocs:bytes   -- total bytes allocated (TotalAlloc)
- /gc/heap/allocs:objects -- total objects allocated (Mallocs - [tiny])
- /gc/heap/frees:bytes    -- total bytes frees (TotalAlloc-HeapAlloc)
- /gc/heap/frees:objects  -- total objects freed (Frees - [tiny])

This change also updates the descriptions of allocs-by-size and
frees-by-size to be more precise.

Change-Id: Iec8c1797a584491e3484b198f2e7f325b68954a7
Reviewed-on: https://go-review.googlesource.com/c/go/+/312431
Reviewed-by: Michael Pratt <mpratt@google.com>
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

src/runtime/metrics.go

@@ -98,6 +98,20 @@ func initMetrics() {
 				}
 			},
 		},
+		"/gc/heap/allocs:bytes": {
+			deps: makeStatDepSet(heapStatsDep),
+			compute: func(in *statAggregate, out *metricValue) {
+				out.kind = metricKindUint64
+				out.scalar = in.heapStats.totalAllocated
+			},
+		},
+		"/gc/heap/allocs:objects": {
+			deps: makeStatDepSet(heapStatsDep),
+			compute: func(in *statAggregate, out *metricValue) {
+				out.kind = metricKindUint64
+				out.scalar = in.heapStats.totalAllocs
+			},
+		},
 		"/gc/heap/frees-by-size:bytes": {
 			deps: makeStatDepSet(heapStatsDep),
 			compute: func(in *statAggregate, out *metricValue) {
@@ -110,6 +124,20 @@ func initMetrics() {
 				}
 			},
 		},
+		"/gc/heap/frees:bytes": {
+			deps: makeStatDepSet(heapStatsDep),
+			compute: func(in *statAggregate, out *metricValue) {
+				out.kind = metricKindUint64
+				out.scalar = in.heapStats.totalFreed
+			},
+		},
+		"/gc/heap/frees:objects": {
+			deps: makeStatDepSet(heapStatsDep),
+			compute: func(in *statAggregate, out *metricValue) {
+				out.kind = metricKindUint64
+				out.scalar = in.heapStats.totalFrees
+			},
+		},
 		"/gc/heap/goal:bytes": {
 			deps: makeStatDepSet(sysStatsDep),
 			compute: func(in *statAggregate, out *metricValue) {
@@ -337,6 +365,22 @@ type heapStatsAggregate struct {
 
 	// numObjects is the number of live objects in the heap.
 	numObjects uint64
+
+	// totalAllocated is the total bytes of heap objects allocated
+	// over the lifetime of the program.
+	totalAllocated uint64
+
+	// totalFreed is the total bytes of heap objects freed
+	// over the lifetime of the program.
+	totalFreed uint64
+
+	// totalAllocs is the number of heap objects allocated over
+	// the lifetime of the program.
+	totalAllocs uint64
+
+	// totalFrees is the number of heap objects freed over
+	// the lifetime of the program.
+	totalFrees uint64
 }
 
 // compute populates the heapStatsAggregate with values from the runtime.
@@ -344,13 +388,20 @@ func (a *heapStatsAggregate) compute() {
 	memstats.heapStats.read(&a.heapStatsDelta)
 
 	// Calculate derived stats.
-	a.inObjects = uint64(a.largeAlloc - a.largeFree)
+	a.totalAllocs = uint64(a.largeAllocCount)
-	a.numObjects = uint64(a.largeAllocCount - a.largeFreeCount)
+	a.totalFrees = uint64(a.largeFreeCount)
+	a.totalAllocated = uint64(a.largeAlloc)
+	a.totalFreed = uint64(a.largeFree)
 	for i := range a.smallAllocCount {
-		n := uint64(a.smallAllocCount[i] - a.smallFreeCount[i])
+		na := uint64(a.smallAllocCount[i])
-		a.inObjects += n * uint64(class_to_size[i])
+		nf := uint64(a.smallFreeCount[i])
-		a.numObjects += n
+		a.totalAllocs += na
+		a.totalFrees += nf
+		a.totalAllocated += na * uint64(class_to_size[i])
+		a.totalFreed += nf * uint64(class_to_size[i])
 	}
+	a.inObjects = a.totalAllocated - a.totalFreed
+	a.numObjects = a.totalAllocs - a.totalFrees
 }
 
 // sysStatsAggregate represents system memory stats obtained

src/runtime/metrics/description.go

@@ -70,17 +70,50 @@ var allDesc = []Description{
 		Cumulative:  true,
 	},
 	{
-		Name:        "/gc/heap/allocs-by-size:bytes",
+		Name: "/gc/heap/allocs-by-size:bytes",
-		Description: "Distribution of all objects allocated by approximate size.",
+		Description: "Distribution of heap allocations by approximate size. " +
-		Kind:        KindFloat64Histogram,
+			"Note that this does not include tiny objects as defined by " +
+			"/gc/heap/tiny/allocs:objects, only tiny blocks.",
+		Kind:       KindFloat64Histogram,
+		Cumulative: true,
+	},
+	{
+		Name:        "/gc/heap/allocs:bytes",
+		Description: "Cumulative sum of memory allocated to the heap by the application.",
+		Kind:        KindUint64,
 		Cumulative:  true,
 	},
 	{
-		Name:        "/gc/heap/frees-by-size:bytes",
+		Name: "/gc/heap/allocs:objects",
-		Description: "Distribution of all objects freed by approximate size.",
+		Description: "Cumulative count of heap allocations triggered by the application. " +
-		Kind:        KindFloat64Histogram,
+			"Note that this does not include tiny objects as defined by " +
+			"/gc/heap/tiny/allocs:objects, only tiny blocks.",
+		Kind:       KindUint64,
+		Cumulative: true,
+	},
+	{
+		Name: "/gc/heap/frees-by-size:bytes",
+		Description: "Distribution of freed heap allocations by approximate size. " +
+			"Note that this does not include tiny objects as defined by " +
+			"/gc/heap/tiny/allocs:objects, only tiny blocks.",
+		Kind:       KindFloat64Histogram,
+		Cumulative: true,
+	},
+	{
+		Name:        "/gc/heap/frees:bytes",
+		Description: "Cumulative sum of heap memory freed by the garbage collector.",
+		Kind:        KindUint64,
 		Cumulative:  true,
 	},
+	{
+		Name: "/gc/heap/frees:objects",
+		Description: "Cumulative count of heap allocations whose storage was freed " +
+			"by the garbage collector. " +
+			"Note that this does not include tiny objects as defined by " +
+			"/gc/heap/tiny/allocs:objects, only tiny blocks.",
+		Kind:       KindUint64,
+		Cumulative: true,
+	},
 	{
 		Name:        "/gc/heap/goal:bytes",
 		Description: "Heap size target for the end of the GC cycle.",

src/runtime/metrics/doc.go

@@ -61,10 +61,30 @@ Below is the full list of supported metrics, ordered lexicographically.
 		Count of all completed GC cycles.
 
 	/gc/heap/allocs-by-size:bytes
-		Distribution of all objects allocated by approximate size.
+		Distribution of heap allocations by approximate size.
+		Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
+		only tiny blocks.
+
+	/gc/heap/allocs:bytes
+		Cumulative sum of memory allocated to the heap by the application.
+
+	/gc/heap/allocs:objects
+		Cumulative count of heap allocations triggered by the application.
+		Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
+		only tiny blocks.
 
 	/gc/heap/frees-by-size:bytes
-		Distribution of all objects freed by approximate size.
+		Distribution of freed heap allocations by approximate size.
+		Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
+		only tiny blocks.
+
+	/gc/heap/frees:bytes
+		Cumulative sum of heap memory freed by the garbage collector.
+
+	/gc/heap/frees:objects
+		Cumulative count of heap allocations whose storage was freed by the garbage collector.
+		Note that this does not include tiny objects as defined by /gc/heap/tiny/allocs:objects,
+		only tiny blocks.
 
 	/gc/heap/goal:bytes
 		Heap size target for the end of the GC cycle.

src/runtime/metrics_test.go

@@ -42,6 +42,7 @@ func TestReadMetrics(t *testing.T) {
 	// Check to make sure the values we read line up with other values we read.
 	var allocsBySize *metrics.Float64Histogram
 	var tinyAllocs uint64
+	var mallocs, frees uint64
 	for i := range samples {
 		switch name := samples[i].Name; name {
 		case "/memory/classes/heap/free:bytes":
@@ -87,6 +88,8 @@ func TestReadMetrics(t *testing.T) {
 				}
 			}
 			allocsBySize = hist
+		case "/gc/heap/allocs:bytes":
+			checkUint64(t, name, samples[i].Value.Uint64(), mstats.TotalAlloc)
 		case "/gc/heap/frees-by-size:bytes":
 			hist := samples[i].Value.Float64Histogram()
 			// Skip size class 0 in BySize, because it's always empty and not represented
@@ -101,6 +104,8 @@ func TestReadMetrics(t *testing.T) {
 					t.Errorf("histogram counts do not match BySize for class %d: got %d, want %d", i, c, f)
 				}
 			}
+		case "/gc/heap/frees:bytes":
+			checkUint64(t, name, samples[i].Value.Uint64(), mstats.TotalAlloc-mstats.HeapAlloc)
 		case "/gc/heap/tiny/allocs:objects":
 			// Currently, MemStats adds tiny alloc count to both Mallocs AND Frees.
 			// The reason for this is because MemStats couldn't be extended at the time
@@ -112,6 +117,13 @@ func TestReadMetrics(t *testing.T) {
 			// Check tiny allocation count outside of this loop, by using the allocs-by-size
 			// histogram in order to figure out how many large objects there are.
 			tinyAllocs = samples[i].Value.Uint64()
+			// Because the next two metrics tests are checking against Mallocs and Frees,
+			// we can't check them directly for the same reason: we need to account for tiny
+			// allocations included in Mallocs and Frees.
+		case "/gc/heap/allocs:objects":
+			mallocs = samples[i].Value.Uint64()
+		case "/gc/heap/frees:objects":
+			frees = samples[i].Value.Uint64()
 		case "/gc/heap/objects:objects":
 			checkUint64(t, name, samples[i].Value.Uint64(), mstats.HeapObjects)
 		case "/gc/heap/goal:bytes":
@@ -131,6 +143,10 @@ func TestReadMetrics(t *testing.T) {
 		nonTinyAllocs += c
 	}
 	checkUint64(t, "/gc/heap/tiny/allocs:objects", tinyAllocs, mstats.Mallocs-nonTinyAllocs)
+
+	// Check allocation and free counts.
+	checkUint64(t, "/gc/heap/allocs:objects", mallocs, mstats.Mallocs-tinyAllocs)
+	checkUint64(t, "/gc/heap/frees:objects", frees, mstats.Frees-tinyAllocs)
 }
 
 func TestReadMetricsConsistency(t *testing.T) {
@@ -153,8 +169,10 @@ func TestReadMetricsConsistency(t *testing.T) {
 		got, want uint64
 	}
 	var objects struct {
-		alloc, free *metrics.Float64Histogram
+		alloc, free             *metrics.Float64Histogram
-		total       uint64
+		allocs, frees           uint64
+		allocdBytes, freedBytes uint64
+		total, totalBytes       uint64
 	}
 	var gc struct {
 		numGC  uint64
@@ -180,10 +198,20 @@ func TestReadMetricsConsistency(t *testing.T) {
 		switch samples[i].Name {
 		case "/memory/classes/total:bytes":
 			totalVirtual.got = samples[i].Value.Uint64()
+		case "/memory/classes/heap/objects:bytes":
+			objects.totalBytes = samples[i].Value.Uint64()
 		case "/gc/heap/objects:objects":
 			objects.total = samples[i].Value.Uint64()
+		case "/gc/heap/allocs:bytes":
+			objects.allocdBytes = samples[i].Value.Uint64()
+		case "/gc/heap/allocs:objects":
+			objects.allocs = samples[i].Value.Uint64()
 		case "/gc/heap/allocs-by-size:bytes":
 			objects.alloc = samples[i].Value.Float64Histogram()
+		case "/gc/heap/frees:bytes":
+			objects.freedBytes = samples[i].Value.Uint64()
+		case "/gc/heap/frees:objects":
+			objects.frees = samples[i].Value.Uint64()
 		case "/gc/heap/frees-by-size:bytes":
 			objects.free = samples[i].Value.Float64Histogram()
 		case "/gc/cycles:gc-cycles":
@@ -203,6 +231,12 @@ func TestReadMetricsConsistency(t *testing.T) {
 	if totalVirtual.got != totalVirtual.want {
 		t.Errorf(`"/memory/classes/total:bytes" does not match sum of /memory/classes/**: got %d, want %d`, totalVirtual.got, totalVirtual.want)
 	}
+	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 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)
+	}
 	if b, c := len(objects.alloc.Buckets), len(objects.alloc.Counts); b != c+1 {
 		t.Errorf("allocs-by-size has wrong bucket or counts length: %d buckets, %d counts", b, c)
 	}
@@ -222,17 +256,25 @@ func TestReadMetricsConsistency(t *testing.T) {
 			}
 		}
 		if !t.Failed() {
-			got, want := uint64(0), objects.total
+			var gotAlloc, gotFree uint64
+			want := objects.total
 			for i := range objects.alloc.Counts {
 				if objects.alloc.Counts[i] < objects.free.Counts[i] {
 					t.Errorf("found more allocs than frees in object dist bucket %d", i)
 					continue
 				}
-				got += objects.alloc.Counts[i] - objects.free.Counts[i]
+				gotAlloc += objects.alloc.Counts[i]
+				gotFree += objects.free.Counts[i]
 			}
-			if got != want {
+			if got := gotAlloc - gotFree; got != want {
 				t.Errorf("object distribution counts don't match count of live objects: got %d, want %d", got, want)
 			}
+			if gotAlloc != objects.allocs {
+				t.Errorf("object distribution counts don't match total allocs: got %d, want %d", gotAlloc, objects.allocs)
+			}
+			if gotFree != objects.frees {
+				t.Errorf("object distribution counts don't match total allocs: got %d, want %d", gotFree, objects.frees)
+			}
 		}
 	}
 	// The current GC has at least 2 pauses per GC.