[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] Design question for PV superpage support



On 03/02/09 10:00, Dave McCracken wrote:
No, actually, it doesn't do that. The hypervisor allocates 2M pages, then expands them into 4K pages for the mfn<->pfn maps, etc.

The only effective difference is that any given 2M-aligned range of pfns is guaranteed to map to a contiguous 2M-aligned range of mfns. Therefore the guest can safely allocate 2M pages.
Ok. So I want to re-iterate my question from a previous post. After the patch allowing mixed mappings, what exactly went wrong on save/restore. And would my special case of 1-1 physival/virtual mappings with additional 2MB VM mappings adddress after domain start suffer in that case?

From my (brief) experience, I think the problems of finding enough contiguous machine memory to allocate an all 2MB domain might be prohibitive. And when the memory is not fragmented I did not find it hard to "find" contiguous aligned 2MB machine pages even with the usual (seemingly random) pfn -> mfn mappings. It's a bit more code and runtime overhead, but it doesn't happen enough to worry about that.

Mick



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.