Blocking on allocation failure - WTF?

The point is that malloc never does block indefinitely with overcommit enabled. It (essentially) always succeeds, and what blocks indefinitely is when you try to write to that shiny new virtual address space that was provided to you by malloc. At this point, the kernel realizes that there aren't any pages to provide you with, but it's too late for malloc to do anything to help you out, since malloc already succeeded.