Re: [Xen-ia64-devel] Pagesize for XEN

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Fri, Jul 27, 2007 at 12:00:41PM +0200, Juergen Gross wrote:

> To avoid any performance degradation for linux or windows guests, my plan is
> to introduce a per-domain or per-vcpu minimal page size. A domain would start
> with the default pagesize (currently 16kB) and in case of usage of a smaller
> page (either via itc, itr or vhpt) the hypervisor should switch to the new
> size by reorganizing the xen-vhpt's of that domain (e.g. doing an implicit
> ptc and setting the new minimal pagesize).

Xen/IA64 truncates down tlb page size when > xen page size, 
on the other hand it doesn't truncate up tlb page size when < xen page size.
So I expect that it needs minor fixes with respect to MMU virtualization.
In theory it should work, however in practice you may encounter issues.


> I'm not sure how to handle grantpages, however. After a quick look into the
> sources I think the pagesize of grantpages is statically defined in the XEN
> configuration (16kB default).
> The cleanest solution would be to add the pagesize for grantpages to the
> interfaces of XEN. On the other hand this would require lots of changes in
> domU and dom0 in architecture independent code.
> So for the moment I will stay with a XEN defined pagesize of grantpages.
> Any problem related to different domU and grantpage pagsizes will be specific
> to the domU using a smaller than default pagesize. As there is no such domU
> up to now, this is just another topic which has to be addressed during the
> "XENification" of the (new) domU.

probably xencomm may need revise.
I'm not sure domU uses a hypercall which requires xencomm conversion, though.

-- 
yamahata

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