Re: [Xen-ia64-devel] [RFC] grant table API clean up and performancetuning memo

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Jeudi 27 Avril 2006 10:40, Isaku Yamahata a écrit :
> On Thu, Apr 27, 2006 at 09:34:54AM +0200, Tristan Gingold wrote:
> > Le Jeudi 27 Avril 2006 04:31, Isaku Yamahata a écrit :
> > [...]
> >
> > > > Two questions:
> > > > It seems your mechanism still need to trust the domains.  So we need
> > > > to add checks for itc/ptc.
> > > >
> > > > However, can a granted page be mapped several times ?
> > > > If so, tracking is necessary and has a cost.
> > >
> > > Grant table API allows it. Xen tracks it by the counter(act->pin).
> > > However current xenLinux maps one-time per a granted page, I believe.
> >
> > Even if it is mapped only once in guest physical memory, it may still be
> > mapped many times in virtual memory.  True ?
>
> Yes, it's true.
> Usually only __va()'ed address is used.
That's certainly true for vbd.  For vnif, if the buffer is allocated from the 
slab, it may then be wrong.  For balloon, this is not true.

I am trying to understand what can be done to avoid global vtlb flush.

Tracking tlb insert is a possible solution, but has an high cost.

Enforcing one insert policy is an easier solution: each page granted may only 
be mapped once in virtual memory.  But this doesn't work for transfer.

I also suppose ballooning is not very frequent and thus global vtlb flush can 
be used when page are removed.  Is it correct ?

Tristan.




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