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.numObjects = uint64(a.largeAllocCount - a.largeFreeCount)
+	a.totalAllocs = uint64(a.largeAllocCount)
+	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])
-		a.inObjects += n * uint64(class_to_size[i])
-		a.numObjects += n
+		na := uint64(a.smallAllocCount[i])
+		nf := uint64(a.smallFreeCount[i])
+		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