Re: [Xen-devel] Is shadow 2 mechanism supported in Xen 3.1?

[Tim Deegan <tim@xxxxxxx>]

Hi, 

At 23:35 +0800 on 08 Mar (1331249756), peng yang wrote:
> I wonder if shadow 2 is supported in Xen 3.1.

Yes.

> This is important because only shadow 2 emulated every write to guest
> pagetables. If so, I can count the exact number of pages belong to a
> process and calculate the memory usage of every process.

Sadly, not.  Shadow 2 emulates all writes to _shadowed_ pagetables, but
there's no guarantee that all pagetables will be shadowed.  Pagetables
that haven't been used by the guest yet won't be shadowed yet.  Also,
there's only a finite amount of shadow memory, so less-recently-used
pagetables get un-shadowed to make room.  (A related problem is that Xen
can't always tell when a page has stopped being a pagetable, so just
because it's shadowed doesn't meen it's definitely a pagetable).

> Besides, I wonder once this counting number drops to zero, can I absolutely
> assume that the process exits.

No, for the same reason.

Cheers,

Tim.

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