RE: [Xen-devel] Memory limits?

["M.A. Williamson" <maw48@xxxxxxxxx>]

> The 4GB limitation mentioned here is for guests. What about the host?
> Does the same limitation apply to the host?
Yes. Which is to say, memory over and above 4Gig won't be usable (although 
the system would obviously still boot).
> If yes... Could you tell me
> how much effort is involved in enabling PAE mode in 32-bit Xen?
I think the concensus was that it wasn't hugely difficult (relative to 
other tasks in the VM system, i.e. would probably still require an 
experienced kernel hacker) but that it would be a bit too time consuming to 
justify the effort required.
> What
> components would need to be modified?
Take a look under xen/arch/x86/x86/mm.c. You'd need to update this to deal 
with the i686 PAE case, as well as the existing i386 and x86_64 page table 
layouts. I heard there was some commonality between i686 PAE and x86_64 
page tables but I don't know how much.
You'd also need to poke around in the Linux memory management code. You'll 
have to pull in PAE support from x86 Linux, modifying the files to Xen-ify 
them.
You might need to modify some of the userspace tools to understand PAE and 
probably some other bits and bobs within Xen.
It's worth emphasising again that Xen *will* support memory > 4gig on the 
upcoming x86_64 port (as well as the IA64 port and other suitable ports).
Cheers,
Mark

> Aravindh
>
> -----Original Message-----
> From: xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx
> [mailto:xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Mark
> Williamson
> Sent: Monday, February 21, 2005 5:57 PM
> To: xen-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: Rene Auberger
> Subject: Re: [Xen-devel] Memory limits?
>
> > I am relatively new to Xen and have a question regarding memory: I was
> not
> > able to find out what the limit of memory is I can assign to a guest
> > system. How much memory can I assign to each guest:
>
> > * not more than physical memory in the machine?
>
> Yes, Xen doesn't do swapping.  If swapping is needed, the guests should
> be 
> configured to do it themselves.
> > * not more than physical memory minus memory used by dom0 and other
> doms?
>
> Correct.  Bear in mind Xen uses some memory too.
>
> > * not more than 4GB?
>
> Correct, on x86 we don't support the PAE36 mode required to support more
> than 
> 4GB.  This is not an insurmountable technical limitation, it's just that
> it's 
> not deemed worth the development time.  On other systems (e.g. x86_64), 
> larger memories does not have the same problems.
> Cheers,
> Mark
>
> > * something totally different?
> >
> > By the way: I am using SuSE 9.2 with the Xen packages from
> > http://www.suse.de/~garloff/linux/xen/ - don't know if that has any
> > influence on which answer applies to my question.
> >
> > Rene
> > ______________________________________________________________
> > Verschicken Sie romantische, coole und witzige Bilder per SMS!
> > Jetzt bei WEB.DE FreeMail: http://f.web.de/?mc=021193
> >
> >
> >
> > -------------------------------------------------------
> > SF email is sponsored by - The IT Product Guide
> > Read honest & candid reviews on hundreds of IT Products from real
> users.
> > Discover which products truly live up to the hype. Start reading now.
> > http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.sourceforge.net/lists/listinfo/xen-devel
>
>
> -------------------------------------------------------
> SF email is sponsored by - The IT Product Guide
> Read honest & candid reviews on hundreds of IT Products from real users.
> Discover which products truly live up to the hype. Start reading now.
> http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxxxx
> https://lists.sourceforge.net/lists/listinfo/xen-devel

-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/xen-devel