Re: [Xen-devel] Need help with fixing the Xen waitqueue feature

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Wed, Nov 9, 2011 at 9:21 PM, Andres Lagar-Cavilla
<andres@xxxxxxxxxxxxxxxx> wrote:
> PoD also does emergency sweeps under memory pressure to identify zeroes,
> that can be easily implemented by a user-space utility.

PoD is certainly a special-case, hypervisor-handled version of paging.
 The main question is whether a user-space version can be made to
perform well enough.  My guess is that it can, but it's far from
certain.  If it can, I'm all in favor of making the paging handle PoD.

> The hypervisor code keeps a list of 2M superpages -- that feature would be
> lost.

This is actually pretty important; Windows scrubs memory on boot, so
it's guaranteed that the majority of the memory will be touched and
re-populated.

> But I doubt this would fly anyways: PoD works for non-ept modes, which I
> guess don't want to lose that functionality.

Is there a particular reason we can't do paging on shadow code? I
thought it was just that doing HAP was simpler to get started with.
That would be another blocker to getting rid of PoD, really.

 -George

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