[Xen-ia64-devel] Pagesize for XEN

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxxxxxxx>]

Hi,

for our mainframe operating system we need support of 4kB pagesize in XEN.
I plan to do some patches to achieve this in the next 2 or 3 weeks.

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).

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.

Comments?

Juergen

-- 
Juergen Gross                             Principal Developer
IP SW OS6                      Telephone: +49 (0) 89 636 47950
Fujitsu Siemens Computers         e-mail: juergen.gross@xxxxxxxxxxxxxxxxxxx
Otto-Hahn-Ring 6                Internet: www.fujitsu-siemens.com
D-81739 Muenchen         Company details: www.fujitsu-siemens.com/imprint.html

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