DEV Community

Ninad Mhatre
Ninad Mhatre

Posted on • Edited on

Rust: cargo release flags or codegen options

#rust #cargo #release #newbie

I am learning Rust actively since a last 6 months, In order to learn I am building small personal projects to learn aspects of language. As I mentioned, I am still a newbie in Rust, so when Microsoft released edit (vim like editor) for windows which is fully written in Rust, I decided to take a look at the code base (I love open-source) in order to learn from it.

First thing I looked at was Cargo.toml and I was surprised by optimizations done for release build.

I decided to try those on my personal project. I created this small utility to parse parquet files using Rust (https://github.com/ninadmhatre/rupy/tree/main/pq). It works but problem is the binary size. Its massive 56 MB! I wanted to see how much reduction can be done on the binary size with this optimization/flags.

Default 

Compilation Time: 2m 10s
Binary Size (MB): 56
Enter fullscreen mode Exit fullscreen mode

Reduce codegen-units

For faster compilation code units are split, default is 256 (incremental) and 16. Higher the number quick the build but may produce slower code. Lets set it 1.

Docs: Here

Flags:

  • codegen-units=1 
Compilation Time: 3m 10s
Binary Size (MB): 40
Enter fullscreen mode Exit fullscreen mode

Change lto

Defers LTO optimizations to linker. Default is no or off.

Docs: Here

Flags:

  • codegen-units=1
  • lto= true 
Compilation Time: 5m 16s
Binary Size (MB): 38
Enter fullscreen mode Exit fullscreen mode

Change opt-level

Controls optimization levels. Default is no optiomization.

Docs: Here

Flags:

  • codegen-units=1
  • lto= true
  • opt-level = "s" // optimize for size 
Compilation Time: 4m 35s
Binary Size (MB): 28
Enter fullscreen mode Exit fullscreen mode

Rest of the flags

Below flags are about debug and controlling behaviour, so instead of checking 1 by 1, I applied them together.

panic: abort or unwind on panic?
strip: Controlles stripping of debuginfo and other data from binary.
split-debuginfo: emitting debuginfo into separate file

Flags:

  • codegen-units=1
  • lto= true
  • opt-level = "s" // optimize for size
  • panic=abort // do not unwind on panic
  • strip="symbols" // if you want crash reporting, then not recommended
  • split-debuginfo="packed" 
Compilation Time: 3m 56s
Binary Size (MB): 20
Enter fullscreen mode Exit fullscreen mode

My repository is very small but depends on Polars. In conclusion, with codegen options/release flags, my compilation time increased to 3m 56s from 2m 10s -> +81% but my binary size reduced from 56M -> 20M -> -65%. You can play around with these options to figure out what works for you.

You can read more about all codegen options

Top comments (0)