Switch to an alternative memory allocator in rustc

[umbrageodotus]

Hey!

In mimalloc 3.x, the max-rss regression has been fixed - meaning it SHOULD be better than jemalloc now. Another alternative worth considering is https://github.com/mjansson/rpmalloc/

Thanks,
Alex <3

[Noratrieb]

That sounds exciting, max-rss was very much what was blocking us from mimalloc. Would you be interested in trying to reland the mimalloc PR with the new version?

[umbrageodotus]

Yes, please! I'd love to! Could you just tell me how to make a performance test PR?

[Kivooeo]

We have a bot that can check your pr for performance, so just make sure it works and file us a PR (example)

[umbrageodotus]

Maybe https://github.com/Microsoft/snmalloc could also work?