Re: is any virtual address space reserved?

From: Rik van Riel (
Date: Fri Sep 20 2002 - 17:11:15 EST

On Fri, 20 Sep 2002, Russ Lewis wrote:

> 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



Bravely reimplemented by the knights who say "NIH".

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