prim → os → arena → page → alloc
alloc: “front-end”: main allocation and free functions.
arena: “back-end”: management of large memory arenas allocated from the OS.
heap: initialization, first-class heaps, thread local theaps, and subprocesses.
prim: primitive functions needed from the host, and OS level allocations.
profile: sampling for guarded allocations, profiled allocations, and the default profiler.
util: utility functions, libc, options, random numbers, statistics, and dynamic thread locals.