Yay for Clang

musl does return memory to the kernel. See free at https://git.musl-libc.org/cgit/musl/tree/src/malloc/mallo... I haven't read closely enough to really understand the heuristics, or the general architecture for that matter, but off-the-cuff I'd guess it's pretty aggressive, but not stupid aggressive. It shouldn't be too difficult to explore. The code is incredibly short compared to ptmalloc, etc; not just free.c, but all of mallocng/.