[mrkline]

- Like others have said, both malloc()/free() touch a lot of global state, so you either have contention between threads, or do as jemalloc does and keep thread-local pools that you occasionally reconcile.

- A moving (and ideally, generational) GC means that you can recompact the heap, making malloc() little more than a pointer bump.

- This also suggests subsequent allocations will have good locality, helping cache performance.

Manual memory management isn't magically pause-free, you just get to express some opinion about where you take the pauses. And I'll contend that (A) most programmers aren't especially good at choosing when that should be, and (B) lots (most?) software cares about overall throughput, so long as max latency stays under some sane bound.