Re: [patch 0/6] Guest page hinting version 6.

[Jeremy Fitzhardinge]

Zachary Amsden wrote:
> On Thu, 2008-03-13 at 18:55 +0000, Hugh Dickins wrote:
>   
> > On Thu, 13 Mar 2008, Jeremy Fitzhardinge wrote:
> >     
> > > My other concern is just correctness over time on the Linux side.  We already
> > > have enough trouble keeping things like the pte and page structure state in
> > > sync, with resulting rare data-loss bugs.  Adding another layer which only
> > > applies in specific environments raises the possibility for new bugs to be
> > > un-noticed for a long time.  How can we structure the VM changes to make sure
> > > that its robust in the face of maintenance?
> > >       
> > Yes, that's the main concern, as whenever lots of subtlety is added.
> > I wonder if there's any chance of a CONFIG_DEBUG mode, which could be
> > run on anybody's x86 machine, without involving any virtualization, but
> > in which the PAGE_STATEs become essential to the correct working of the mm.
> >     
>
> How about a fake hypervisor, which is really just a random page evictor,
> following the rules of CMM?
>   

Probably simpler to just have variants of the page_set_* functions which 
simulate the worst-possible host action immediately (ie, stealing pages, 
logically swapping them, etc).  That wouldn't give you full coverage, 
but it would go some way.  An async variant which schedules a change in 
a few milliseconds would help too.

I guess that's equivalent to having a special-purpose hypervisor built 
into the kernel (hm, sounds familiar...).

   J
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