On Thu, 2006-09-14 at 02:23 -0700, Zachary Amsden wrote:

Martin Schwidefsky wrote

quoted

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.

The mainframes have that trick in hardware for about 30 years ..

quoted

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.

I wonder which trick you use, since there is only one page table one
i386 I can only imagine that you are tracking all page tables of the
guest.

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.

I've been sitting on these patches for months now and you are worrying
about two weeks..

-- 
blue skies,
  Martin.

Martin Schwidefsky
Linux for zSeries Development & Services
IBM Deutschland Entwicklung GmbH

"Reality continues to ruin my life." - Calvin.