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dictionary - How to get memory size of variable in Go?

I am curious about the memory cost of map and slice, so I wrote a program to compare the sizes. I get the memory size by unsafe.Sizeof(s), but obviously it is wrong, because when I change the size, the output is the same.

func getSlice(size int) []int {
    t := time.Now()
    s := make([]int, size*2)
    for i := 0; i < size; i++ {
        index := i << 1
        s[index] = i
        s[index+1] = i
    }
    fmt.Println("slice time cost: ", time.Since(t))
    return s
}

func getMap(size int) map[int]int {
    t := time.Now()
    m := make(map[int]int, size)
    for i := 0; i < size; i++ {
        m[i] = i
    }
    fmt.Println("map time cost: ", time.Since(t))
    return m
}

func TestMem(t *testing.T) {
    size := 1000
    s := getSlice(size)
    m := getMap(size)
    fmt.Printf("slice size: %d
", unsafe.Sizeof(s))
    fmt.Printf("map size: %d
", unsafe.Sizeof(m))
}
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