Re: Xen at scale

[Kip Macy <kmacy@fsmware.com>]

On FreeBSD i386, there is already a 4MB chunk of VA where the page
tables are mapped - remember that is why the PTD maps itself (as the comment
puts it, recursively). This is the default layout
|  USER         |PTs| KVA     |
  (3GB - 4M)     4M   1GB

I've allocated an extra page-table to the PTOM - for the following VA:

| USER        |PTOM|PTs|  KVA|
  3GB - 8M      4M   4M  1GB

This works well, because all I end up having to do is bump down
VM_MAXUSER_ADDRESS by an extra 4MB. Putting it in the kernel would
disrupt pmap bootstrap. This burns some VA for small memory allocations,
but the same can be said for the PTs and it makes easy for me to put the
PTOM on a single super-page for large memory allocations.

As for DOM0, different guests can have their own setup routines inside Xen.


			-Kip

On Wed, 24 Mar 2004, Christian Limpach wrote:

> > It needs to be something other than page tables, really. I'm inclined
> > to pass the new domain a preinitialised 'phys->machine' translation
> > table, and only create initial page tables large enough to contain the
> > kernel image, initial page tables, and the translation table. 16MB of
> > VA space would be plenty.
>
> VA should probably have the size of text+data+bss.  My preferred layout
> would be pagetables/pgd/p2m-mapping at the end of the domain's physical
> memory in that order.  And this should then be either mapped at VA 0, end
> aligned with text or end aligned with the hypervisor memory.  I think I'd
> choose end aligned with the hypervisor memory.
>
> > As for breaking the interface to other types of guest OS
> > (ie. non-Linux) -- they can implement their own domain builder that
> > sets memory out just as they like.
>
> How's that supposed to work for non-Linux domain0 guests?
>
>      christian
>
>
>
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