For what it's worth, while playing with mimalloc I added support for applying local patches to upstream: https://github.com/DataDog/mimalloc_rust/tree/ivoanjo/mimalloc-tweaks .

E.g. https://github.com/DataDog/mimalloc_rust/blob/ivoanjo/mimalloc-tweaks/libmimalloc-sys/build.rs calls into https://github.com/DataDog/mimalloc_rust/blob/ivoanjo/mimalloc-tweaks/libmimalloc-sys/build_custom.rs which then applies every patch in https://github.com/DataDog/mimalloc_rust/tree/ivoanjo/mimalloc-tweaks/libmimalloc-sys/patches before building.

This was only a side-project so I paused the work, but if it would be useful, I'd be happy to open a PR to add this support for patches?

Hey
Thanks, I'm also trying to get this change upstreamed (microsoft/mimalloc#1066)

No worries! Thanks for working on mimalloc_rust, it was really useful in getting my experiments off the ground quickly 🙏