Re: recommendations for a Xen/NetBSD box?

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Sun, Feb 24, 2008 at 01:45:04PM +1100, Carl Brewer wrote:
> >I believe it's something like Physical Address Extension.  Roughly
> >speaking, it lets you have more than 32 bits of phyiscal memory, even
> >on a 32-bit i386.
> 
> Thanks Steve, I grabbed that from the Xen user guide just after 
> replying.  As the box only has 4GB and I'm planning on giving 2GB to the 
> main NetBSD 4.0 instance, and the CentOS instance only needs maybe 1GB 
> or so, I don't think I need it?

Without PAE, you'll have something like 3GB useable, maybe a bit more.
memory-mapped PCI devices are mapped at the top of the 32bit physical
address space, and the corresponding physical ram is mapped above 4GB.
How much space is needed by memory-mapped PCI devices depends on the
number of PCI devices and the chipset; but it's between 512MB and 1GB.

> Do the DomU's need to know about it if 
> the Dom0 is managing memory for them?

For Xen guests yes, because the physical format of the page tables is
different. HVM guests can run either a 32bit kernel, or a 32bitPAE kernel
if the dom0 knows about PAE

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--