[quotemstr]

Malloc can also fail if you're out of address space without necessarily being out of memory.

NT does a much better job of separating these concepts than Unix-family operating systems do. Conceptually, setting aside a region of your process's address space and guaranteeing that the OS will be able to serve you a given number of pages are completely different operations. I wish more programs would use MAP_NORESERVE when they want the former without the latter. (I'm looking at you, Java.)

One day, perhaps when I am old and frail, we will achieve sanity and turn overcommit off by default. But we're a long way from being able to do that now.

[klodolph]

These days, I describe malloc() as "a function which allocates address space", to avoid confusion. Which means it makes sense that malloc() returns NULL if you are out of address space, even if you have lots of memory. (But so many people don't check malloc()'s return anyway...)