Sure. I'm just saying that the kernel doesn't have some kind of magic capability that lets it zero memory faster than userspace can. It does have a small free-l

Sure. I'm just saying that the kernel doesn't have some kind of magic capability that lets it zero memory faster than userspace can. It does have a small free-list of already-zero pages, granted, but a really big allocation will deplete that list, and that list needs to be replenished somehow. For Linux, I want to grant MAP_UNINITIALIZED access to unprivileged users (keep reading) but actually zero pages it gives to these unprivileged MAP_UNINITIALIZED --- users unless it knows that a page doesn't contain privileged information. For example, if a process munmap()s a particular region and then immediately mmap()s a different one, and no other process has ever mapped that page, there's no harm in allowing the process to see its own previous page content.