> Is any of a userland application's virtual address space reserved?
> Certainly, some memory is used at startup: the code is loaded into some
> of the virtual space, as well as the stack. There needs to always be
> enough space for the stack to grow as necessary. But is any of the
> space actually marked off as "reserved"? If we just mmap'ed the same
> file over and over again, could we fill the 4Gb address space with
> identical mappings, or would we run out?
There are a number of issues here:
1) userspace has 3 GB space, kernel has the other 1 GB
2) if you want to mmap a file over and over again, you'll
need to have the code that maps the file and the glibc
mmap(3) stuff mapped into your address space ;)
3) your process will want to have a stack somewhere
4) address 0 is reserved to trap NULL pointer dereferences
both in kernel and user space
cheers,
Rik
-- Bravely reimplemented by the knights who say "NIH".http://www.surriel.com/ http://distro.conectiva.com/
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