A comment from Hugh Dickins:
I remember thinking that the idea of data ulimit had become obsolete (just preserved for compatibility) back when mmap() got invented and used for dynamic libraries. I think that's when they brought in RLIMIT_AS, something which could make sense in the mmap() world.
Regardless, this patch does not seem to have made it in: I looked at linux-2.6.36-rc8. A bug was filed about this in 2008, updated most recently in March 2010. And this issue is now also being tracked on Fedora/RedHat's bugzilla.
EDIT: This fortune is relevant.
Note that nobody reads every post in linux-kernel. In fact, nobody who expects to have time left over to actually do any real kernel work will read even half. Except Alan Cox, but he's actually not human, but about a thousand gnomes working in under-ground caves in Swansea. None of the individual gnomes read all the postings either, they just work together really well. -- Linus Torvalds