Heads-up: Requiring PAE for running Xen

[Axel Thimm]

On Sat, May 20, 2006 at 09:47:17AM -0500, Josh Boyer wrote:
> 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.

Not within rawhide, or?

> 
> 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 :).

If personal bits matter, then I'd go for 3. I have no 32 bit machine
with >= 4GB, but quite a few 64 bits ones. And the toy machines I
would use to play with rawhide have no PAE. I guess whoever needs that
much memory also needs something like x86_64' in-chip memory
controller.

(the only systems I've recently seen with large memories running on 32
bits were 64-bits platforms with Debian, due to Debian not supporting
multilib ...)
-- 
Axel.Thimm at ATrpms.net
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