Re: [patch 3/9] Guest page hinting: volatile page cache.

Zachary Amsden
2006-09-14T09:23:40Z

Martin Schwidefsky wrote
> The discard fault happens on access to a volatile that has been
> discarded. An important property of the s390 architecture comes into
> play here: there are two page tables, a guest page table and a host page
> table. What the guest perceives as its "physical" memory is in virtual
> storage for the host. An address resolution has to walk two pages
> tables, if a pte is invalid in either table you get a fault. A guest
> fault if the invalid pte is in the guest table and a host fault if it is
>

Yes, I'm familiar with that trick. Wasn't sure if you had it in
hardware or not.

> in the host table. That gives s390 a simple method to implement
> discarded pages: the hypervisor just unmaps the page from the host table
> and changes the state of the guest page. I can see that you will have a
> much harder time to implement this on i386.
>

Nah, I think we'll do just fine.

Thanks for the info - based on this, I think we can probably use the
volatile page / swap cache changes as well for VMware, also pretty much
unchanged. Sorry to take so long to look at these patches, BTW - I was
on holiday for two weeks.

Zach