Show memory usage in go services

code.go

// From https://github.com/dustin/go-humanize
func intToByte(s uint64) string {
	sizes := []string{"B", "kB", "MB", "GB", "TB", "PB", "EB"}
	base := 1000.0
	logn := func(n, b float64) float64 {
		return math.Log(n) / math.Log(b)
	}

	if s < 10 {
		return fmt.Sprintf("%d B", s)
	}
	e := math.Floor(logn(float64(s), base))
	suffix := sizes[int(e)]
	val := math.Floor(float64(s)/math.Pow(base, e)*10+0.5) / 10
	f := "%.0f %s"
	if val < 10 {
		f = "%.1f %s"
	}

	return fmt.Sprintf(f, val, suffix)
}

func init() {
	// fn, err := os.Create("memory.log")
	// if err != nil {
	// 	panic(err)
	// }
	fn := os.Stdout

	type keyFunc struct {
		key string
		f   func(metrics.Value) any
	}

	metricKeys := []keyFunc{
		{"/memory/classes/heap/free:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/heap/objects:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/heap/released:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/heap/stacks:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/heap/unused:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/metadata/mcache/free:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/metadata/mcache/inuse:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/metadata/mspan/free:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/metadata/mspan/inuse:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/metadata/other:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/os-stacks:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/other:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/profiling/buckets:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/memory/classes/total:bytes", func(v metrics.Value) any { return intToByte(v.Uint64()) }},
		{"/gc/cycles/total:gc-cycles", func(v metrics.Value) any { return v.Uint64() }},
	}

	sampleList := make([]metrics.Sample, len(metricKeys))
	for i, kf := range metricKeys {
		sampleList[i].Name = kf.key
	}

	go func() {
		for {
			// Sample the metric.
			metrics.Read(sampleList)

			fmt.Fprintln(fn, time.Now())
			for i, sample := range sampleList {
				key := sample.Name
				value := metricKeys[i].f(sample.Value)

				fmt.Fprintf(fn, "%s\t\t\t%v\n", key, value)
			}
			fmt.Fprintln(fn)

			time.Sleep(time.Second)
		}
	}()
}