Heads-up: Requiring PAE for running Xen

[Josh Boyer]

On Sat, 2006-05-20 at 16:14 +0200, Axel Thimm wrote:
> On Wed, May 17, 2006 at 02:07:59PM -0400, Jeremy Katz wrote:
> > As we move forward with Xen enablement, there's a desire for
> > being able to access more than 4 gigs of RAM on 32-bit Xen hosts.  The
> > options for handling this are
> > 1) Another kernel.  This is bad due to 
> >    a) we're running out of CD space already
> >    b) keeping things matched up between the HV and the guest kernels
> >    c) migration is worlds of pain with two types of kernels
> > 2) Switch the 32-bit xen kernels to require PAE.  For most "current"
> > non-laptop hardware, this is a non-issue.  It does mean that xen won't
> > work a lot of earlier PentiumM laptops
> > 3) Do nothing, tell people to use 64bit if they want more than 4 gigs of
> > RAM
> > 4) Make the PAE code handled at runtime.  This is a pretty non-trivial
> > amount of work :)
> > 
> > Given these, we're looking at going with #2 and thus only having Xen
> > work on PAE-capable hardware in the development tree.  And we're
> > planning to try to execute this switchover the beginning of next week.
> > Note that this will not affect bare metal installs at all.
> > 
> > Jeremy
> 
> Judging from the feedback I would derive that
> 
> o in later production environments usually hardware with PAE support
>   will be used.
> 
> o during development, though, people would like to test xen on their
>   non-PAE hardware like their laptops.
> 
> So maybe rawhide should continue with both PAE and non-PAE kernels and
> decide on dropping the non-PAE when a release is about to be cut?

I don't think so.  I think you missed the "worlds of pain" part about
having two kernels.  It also becomes a resource issue.

I think option 1 is simply too much burden.  So options 2 and 3 are
left.  It seems to come down to which is the "greater good".  Which
group is larger?  The ones that don't have PAE hardware, or the ones
that have machines with >= 4 gigs of RAM that are non-64bit.

Personally, I think option 2 is fine.  Of course, both my machines have
PAE :).

josh