Seems to be removal of jemalloc
from reading the comments (haven't looked at the actual code) it sounds like:
- we are still using jemalloc in rustc (so it's not the system allocator that causes the regression)
- but jemalloc has been upgrade from 4.x to 5.x
maybe we can tweak some jemalloc settings to better fit rustc's profile
I'm sure that @nnethercote will take a look at this, given that they've spent lots of work on reducing rustc's memory usage.
(if not, someone else should definitely do some profiling)