[OSM-dev] mmap()

[Dave Hansen]

On Fri, 2008-12-05 at 02:25 +0100, Stefan de Konink wrote:
> Sascha Silbe wrote:
> > On Thu, Dec 04, 2008 at 03:20:02PM -0800, Dave Hansen wrote:
> > 
> >>> I don't think that's possible. Both 32bit and 64bit userspace and 
> >>> emulation work with a 64bit kernel, but at least 64bit userspace on a 
> >>> 32bit kernel isn't possible.
> >> Believe it or not, people actually do this on powerpc.
> > Interesting. Is it possible on AMD64 as well? How does the additional 
> > address space get managed?
> > As this is getting off topic, I'd suggest to move to private mails.
> 
> Why would you use a 32bit kernel over a 64bit one on a 64bit arch?

Register contents are half the size.  So, integers and pointers all get
smaller.  That increases cache coverage and decreases the size of
binaries, working sets and the stack.

x86_64 also gets registers over plain i386.  So, the extra register room
can make up for any extra cache footprint.  

-- Dave