mmap guard pages

Solar,

What do you think about this?

http://www.openbsd.org/papers/ven05-deraadt/mgp00025.html

In short, each mmap call adds guard pages before and after the allocated memory. It should catch overflows/underflows of mmap-based buffers. AFAICS, it's possible to painlessly (in terms of vm waste) enable it on x86-64.

Thanks,

Vasiliy