1// run
2
3//go:build amd64
4
5// Copyright 2016 The Go Authors. All rights reserved.
6// Use of this source code is governed by a BSD-style
7// license that can be found in the LICENSE file.
8
9package main
10
11import "runtime"
12
13type big [10 << 20]byte
14
15func f(x *big, start int64) {
16	if delta := inuse() - start; delta < 9<<20 {
17		println("after alloc: expected delta at least 9MB, got: ", delta)
18	}
19	runtime.KeepAlive(x)
20	x = nil
21	if delta := inuse() - start; delta > 1<<20 {
22		println("after drop: expected delta below 1MB, got: ", delta)
23	}
24	x = new(big)
25	if delta := inuse() - start; delta < 9<<20 {
26		println("second alloc: expected delta at least 9MB, got: ", delta)
27	}
28	runtime.KeepAlive(x)
29}
30
31func main() {
32	x := inuse()
33	f(new(big), x)
34}
35
36func inuse() int64 {
37	runtime.GC()
38	var st runtime.MemStats
39	runtime.ReadMemStats(&st)
40	return int64(st.Alloc)
41}
42