Golang memory allocation test

Question

I'm trying to allocate memory with my "program" - just to allocate it and stay there - for testing purposes. When I run it on my MacOS the Activity Monitor shows it allocates 1.6 gb, when I compile it for linux and run it there it does nothing - it prints the message but the ram isn't being used on the machine. Am I doing it wrong? Is there a better way? Here is my code:

package main


import (
    "fmt"
    "unsafe"
    "time"
)


func main() {
    var buffer [100 * 1024 * 1024]string
    fmt.Printf("The size of the buffer is: %d bytes\n", unsafe.Sizeof(buffer))
    time.Sleep(300 * time.Second)
}

First I used byte for my array type, but it did not worked event on my mac?

Answer 1

There's nothing whatsoever in your code that requires memory. The compiler is perfectly within its rights to optimize the whole allocation away, and even if the compiler doesn't do it, the OS will not commit the memory - you're never assigning anything, so it's likely just mirroring a zero-page.

I don't know anything about the subtle differences between whatever Linux you're using and whatever MacOS you're using, so there's little that can be said with certainty. It might very well be that your way of checking memory on your linux machine gives you only committed memory, while you're seeing all virtual memory on your MacOS, or there might be other subtle differences. In any case, since compilers became smart and since we had virtual memory on PCs, it's been getting harder and harder to get any meaningful benchmarks - the tools we work with are usually smart enough to avoid unnecessary waste; and most benchmarks you'll try are pretty much completely unnecessary waste.

Benchmarking is hard.