Re: [Xen-users] 32bit vs 64bit memory usage question

[Geoff Streeter <geoff@xxxxxxxxxx>]

At 2007-02-05 10:00 -0500, Tom Miller wrote:
> Jamie Burns wrote:
> > Hello,
> >
> > I recently installed a minimal 32bit version of Debian Etch, and then 
> > also installed Xen from Debian's package repository.
> > When Xen booted up, memory usage was just below 40MB (typical for such a 
> > debian install).
> > Then I decided to do the exact same install, but using the 64bit version 
> > of Debian Etch and Xen.
> > This time when Xen booted up, memory usage was just over 90MB - at least 
> > double that of the 32bit version.
> > Can anybody explain this to me? Why 64bit XEN would use double the memory?
> >
> > If I try 32bit vs 64bit debian without using XEN, then memory use about 
> > 30MB with each - no doubling.
> > Jamie Burns.
> >
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-users
> 64 bit pointers and 64 bit memory address slots are twice as big as
> corresponding 32 bit ones.   So unless you have 4 GB of memory or more,
> using 64bit software is actually slower for the system, not faster.
>
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users
Sometimes it is more about address space than real memory. Some apps like 
to map very large files. If you have one 64 bit app you NEED to run then 
you have no choice but to run a 64 bit kernel. In addition apps that really 
want to use memory in the range 2-4GB are better implemented using 64 bit.
Geoff Streeter


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