> That said, even on Linux allocators will return NULL when they're just out of address space; there's no overcommit going on there. Try calling fork() in that

> That said, even on Linux allocators will return NULL when they're just out of address space; there's no overcommit going on there. Try calling fork() in that process then. By rights, the new process should inherit its own copy of all the address space of the old process, and is free to overwrite it with whatever it wants. Linux (by default) won't stop fork() from failing on a process with N GB of RAM and total memory(+swap) < 2N GB, yet there simply isn't the memory around for both processes. There's your overcommit.