Both glibc and musl libc still uses brk for most allocations. You can see it when strace'ing simple programs. After the linker--which uses mmap for some allocat

Both glibc and musl libc still uses brk for most allocations. You can see it when strace'ing simple programs. After the linker--which uses mmap for some allocations as it can't use malloc--has finished you'll see brk calls to satisfy application allocations. Also you can verify in the code, e.g. https://git.musl-libc.org/cgit/musl/tree/src/malloc/expand_heap.c?id=55a1c9c8#n56 https://git.musl-libc.org/cgit/musl/tree/src/malloc/expand_h... I believe OpenBSD's malloc only uses mmap and also aggressively munmap's memory--to better catch application bugs and to keep addresses randomized.