Maybe it depends upon the architecture? With a 64 bit address space, there should be plenty of room to allow for a contiguous sbrk-allocated chunk of memory and

Maybe it depends upon the architecture? With a 64 bit address space, there should be plenty of room to allow for a contiguous sbrk-allocated chunk of memory and separate mmap regions that are far away from any possible overlap. 32 bit processes might have to take more precautions to prevent premature address space collisions.