Address Space Layout Randomization, since 2010. Carsten Mattner asked, and Alex Hornung answered. (Set the sysctl vm.randomize_mmap to 1 to enable it.)
vm.randomize_mmap may also improve the performance of certain workloads, particularly mmap/malloc-heavy ones which create many vm_map_entries.
Why is this not on by default today?
DragonFly BSD Digest