On the contrary, fork() has scalability trouble as memory grows. Even with copy on write, copying page tables is still O(1) with respect to address space (grant

On the contrary, fork() has scalability trouble as memory grows. Even with copy on write, copying page tables is still O(1) with respect to address space (granted, with a significant divisor). This overhead becomes apparent as programs grow to gigabyte size -- a fork which before took microseconds can begin to take milliseconds. Forking is slow in many situations. The issue described above can be avoided by using posix_spawn(3), which on linux uses vfork(2).