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?

Measuring "how much memory is used" was a simple task 25 years ago. It is no longer simple as there is a fast amount of different types of "memory". And "used" is a much to vague term for memory. Use the toolage provided by go test -benchmem to see how "allocation heavy" your code is. That metric is more reliable and more important. — Volker
– Volker, Commented Sep 21, 2015 at 11:23

Luaan · Accepted Answer · 2015-09-21 11:22:51Z

5

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.

answered Sep 21, 2015 at 11:22

Luaan

64.1k7 gold badges108 silver badges126 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

plamer Over a year ago

Thanks, I'm just playing around and wanted to see what happens. This: "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" helped :) - I added for e, _ := range buffer { buffer[e] = "string" } and now when I run it on the linux box the mem used gets up with 1.6 gigs.

Collectives™ on Stack Overflow

Golang memory allocation test

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related