Fork is copy-on-write. The problem is that there's no way for fork() to know how much memory the child process needs. It might call exec() immediately, using ve

Fork is copy-on-write. The problem is that there's no way for fork() to know how much memory the child process needs. It might call exec() immediately, using very little memory. It might keep running, mostly sharing pages with the parent. It might touch every memory page, requiring a lot of memory.