Pathological case for blowing up heap profile bucket sizes

README.md

Example run:

% go1.22.6 run .
29764202
% go version
go version go1.23.1 darwin/arm64
% go run .
3001476733

That's an over 100x increase.

deepstacks.go

package main

import (
	"fmt"
	"math/rand"
	"runtime"
	"runtime/metrics"
)

//go:noinline
func garbage() []byte {
	//return make([]byte, rand.Intn(32))
	return make([]byte, 4)
}

//go:noinline
func left(depth int) {
	if depth == 0 {
		garbage()
		return
	}
	if depth < 16 {
		// Keep the leaf end of the stack fixed to blow up the difference
		// with having deeper stacks capture more recursion further up.
		left(depth - 1)
		return
	}
	if rand.Intn(2) == 0 {
		left(depth - 1)
	} else {
		right(depth - 1)
	}
}

//go:noinline
func right(depth int) {
	if depth == 0 {
		garbage()
		return
	}
	if depth < 16 {
		right(depth - 1)
		return
	}
	if rand.Intn(2) == 0 {
		left(depth - 1)
	} else {
		right(depth - 1)
	}
}

func main() {
	runtime.MemProfileRate = 1
	defer func() {
		s := make([]metrics.Sample, 1)
		s[0].Name = "/memory/classes/profiling/buckets:bytes"
		metrics.Read(s)
		fmt.Printf("%v\n", s[0].Value.Uint64())

		// "Read" the profile so profiling doesn't get stripped.
		// These profiles get big so actually serializing them is really slow.
		runtime.MemProfile(nil, false)
	}()

	for range 10000000 {
		depth := 128
		if rand.Intn(2) == 0 {
			left(depth)
		} else {
			right(depth)
		}
	}
}