It's definitely 2.1, if even that. Shared anonymous mmap is a monstrosity
(even the name is a oxymoron), and it's hard to implement to boot.
Use SysV shared memory - it's _also_ a monstrosity (and hard to implement,
but that part has been done already), but at least it has made a _try_ at
making sense from a semantic viewpoint. I'd like to avoid shared anonymous
mmap altogether, although with the current page cache it is at least possible
to do sanely in theory.
Linus