[dexen]

> (...) that most allocators will use brk/sbrk to resize the data segment of the executing process to allocate memory, at least if they shall allocate few memory.

The other commonly used backend for malloc() is mmap() without underlying file:

  void *chunk = mmap(NULL, length, PROT_READ|PROT_WRITE, MAP_ANONYMOUS, -1, 0);

Handy both when allocating large chunks of memory and for allocating pools for smaller suballocations. Has the additional benefit of being zeroed-out at low cost (or no cost at all -- for example via hardware DMA), and also playing nice on systems with constrained / fragmented address space, as kernel is free to allocate at any address visible from userspace.