[go-nuts] It looks making a slice with size 32768+1 will allocate with one memory page as needed

[tapi...@gmail.com]

package allocate

import "testing"
import "os"
import "fmt"

func init() {
    fmt.Println("OS page size:", os.Getpagesize())
}

var r1 []byte

func BenchmarkCount1(b *testing.B) {
    for i := 0; i < b.N; i++ {
        r1 = make([]byte, 32768+1)
    }
}

var r2 []byte

func BenchmarkCount2(b *testing.B) {
    for i := 0; i < b.N; i++ {
        r2 = make([]byte, 40)
    }
}

The output:

OS page size: 32768
BenchmarkCount1-4         166443          7312 ns/op       40960 B/op    
       1 allocs/op
BenchmarkCount2-4       31465389            36.88 ns/op          48 B/op    
       1 allocs/op

In fact, a memory block with size 36864 is enough to carry the elements of 
a byte slice with size 32768+1. Why to allocate one more page for them?

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