Re: Xen at scale

[Christian Limpach <chris@pin.lu>]

> The {DragonFly/Free}BSD domain builder sets the page tables up a little
> differently. It populates the phys_to_machine array before starting
> the domain - mapping it at a pre-determined address relative to
> KERNBASE.

How is it pre-determined?

And where do you put it physically?  I would probably put it at the very end
of the physical address space since the guest is less likely to rebuild the
mapping table than it is likely to rebuild the pagetables.  Every other
place seems to require special handling in the guests memory management...

Having a domain layout which isn't compatible with the Linux one is a
problem if you want to boot your domain as domain0 since the builder for
domain0 is inside Xen.

> > Maybe there's a simpler solution?
>
> I don't think passing an array is more complicated.

It's more complicated because you need to put it somewhere and then most
guests have to possibly move it around because they don't like where it was
put by the builder.  But most of all I think that it's a bad idea to use two
different interfaces to pass the same kind of data and that we should try to
keep the amount of pre-initialized data to a minimum.

It might still be time to switch to using an array but the sooner the better
and then we should stick with whatever we choose...

     christian



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