Funny you should mention that. Recently, glibc 2.38 was released with broken performance in its allocator API. Hell, one of the developers tried to argue the regression is good to force people to stop using the regressed API unnecessarily (the argument didn't go far, regressions got fixed).

Reports in the wild:
https://github.com/mpv-player/mpv/issues/12076
https://bugs.archlinux.org/task/79300

Links to the libc-alpha relevant threads can be found there.

Speaking of libc allocators, musl's allocator is also shit. That's why some Rust projects use another global allocator in their musl builds. Some of them probably haven't noticed yet that those builds are not static anymore because of that 😉 .