memory.md

Memory management and optimization

Measure the size of a scalar value, struct, or array

This approach doesn't follow references.

struct Container<T> {
    items: [T; 3],
}

fn main() {
    use std::mem::size_of_val;

    let cu8 = Container {
        items: [1u8, 2u8, 3u8],
    };
		println!("size of cu8 = {} bytes", size_of_val(&cu8));  // returns 3

    let cu32 = Container {
        items: [1u32, 2u32, 3u32],
    };
    println!("size of cu32 = {} bytes", size_of_val(&cu32));  // returns 12
}

Measure memory consumption programmatically

This will compile and run on Linux.

cargo add jemallocator
cargo add jemalloc-ctl

In your main.rs file add the following global allocator declaration.

#[cfg(not(target_env = "msvc"))]
#[global_allocator]
static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;

In the rust file where you want to measure the memory consumption.

use jemalloc_ctl::{stats, epoch};

// ...
let epoch = epoch::mib().unwrap();
let allocated_mib = stats::allocated::mib().unwrap();

let allocated_before = allocated_mib.read().unwrap();
let _buf = vec![0i64; 16];
epoch.advance().unwrap();
let allocated_after = allocated_mib.read().unwrap();
println!("{} bytes allocated", allocated_after - allocated_before);

Use better memory allocators

These days one of the best memory allocator is mimalloc (Microsoft) followed by glibc 2.31 and jemalloc (Facebook) according to this test and this one.

An Alpine preloaded with mimalloc can be found here.

docker pull emerzon/alpine-mimalloc

ToDo: Find more recent comparison tests.

Change the default Musl memory allocator

The default Musl memory allocator is super slow according to this test. Better to use mimalloc (Microsoft) or jemalloc (Facebook).

cargo add mimalloc

Declare the mimalloc allocator in your main.rs file.

use mimalloc::MiMalloc;

#[global_allocator]
static GLOBAL: MiMalloc = MiMalloc;