Comment by yayachiken

Note that the fork()/execve() semantics of Linux pretty much depend on memory overcommit. You may get weird OOM crashes when there is seemingly no memory pressure, if you turn overcommit off.

In the short time between fork() and execve(), the new process duplicates the entire virtual memory of the old one. None of this is physically allocated due to copy-on-write, but still all counts as virtual memory.