[amelius]

But malloc calls sbrk(), right?

[dwattttt]

I can't speak to multiple users of sbrk, I assume that would fail. That's a property of sbrk though, not of malloc (or memory allocation in general); on Windows, you can have as many implementors of malloc as you want, so long as malloc/free calls happen to the same implementor. Each malloc implementor just asks for anonymous backing pages for their own heaps (via VirtualAlloc/mmap).

[unusual-name]

It depends on the implementation. For example, jemalloc can use sbrk(), sbrk() and mmap() or just mmap(), depending on what your os supports.