How to benchmark memory usage of a function?

Question

I notice that Rust's test has a benchmark mode that will measure execution time in ns/iter, but I could not find a way to measure memory usage.

How would I implement such a benchmark? Let us assume for the moment that I only care about heap memory at the moment (though stack usage would also certainly be interesting).

Edit: I found this issue which asks for the exact same thing.

Answer 1

You can use the jemalloc allocator to print the allocation statistics. For example,

Cargo.toml:

[package] name = "stackoverflow-30869007" version = "0.1.0" edition = "2018"  [dependencies] jemallocator = "0.3" jemalloc-sys = {version = "0.3", features = ["stats"]} libc = "0.2" 

src/main.rs:

use libc::{c_char, c_void}; use std::ptr::{null, null_mut};  #[global_allocator] static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;  extern "C" fn write_cb(_: *mut c_void, message: *const c_char) {     print!("{}", String::from_utf8_lossy(unsafe {         std::ffi::CStr::from_ptr(message as *const i8).to_bytes()     })); }  fn main() {     unsafe { jemalloc_sys::malloc_stats_print(Some(write_cb), null_mut(), null()) }; } 

In a single-threaded program that should allow you to get a good measurement of how much memory a structure takes. Just print the statistics before the structure is created and after and calculate the difference.

---

You can also use Valgrind (Massif) to get the heap profile. It works just like with any other C program. Make sure you have debug symbols enabled in the executable (e.g. using debug build or custom Cargo configuration). You can use, say, http://massiftool.sourceforge.net/ to analyse the generated heap profile.

(I verified this to work on Debian Jessie, in a different setting your mileage may vary).

(In order to use Rust with Valgrind you'll probably have to switch back to the system allocator).

P.S. There is now also a better DHAT.

---

jemalloc can be told to dump a memory profile. You can probably do this with the Rust FFI but I haven't investigated this route.