Re: [Xen-devel] [PATCH 2 of 5] xenpaging: map gfn before nomination

[Tim Deegan <tim@xxxxxxx>]

At 10:27 +0100 on 07 Dec (1323253657), Olaf Hering wrote:
> On Tue, Dec 06, Andres Lagar-Cavilla wrote:
> 
> > Ouch! You're absolutely tying the user space pager with the underlying xen
> > paging code. Most of your patches change the tools and the hypervisor in
> > lockstep.
> 
> Yes, pager and hypervisor are bound closely together.
> 
> > Patch 4 in your series is one such case. Short-cutting the state machine:
> > great. But what is the gain for the hypervisor in *not* sending the
> > EVICT_FAIL event. It's a good thing. It keeps the same interface to
> > user-space. Xenpaging may not need it, but the Xen paging code does not
> > exist solely for xenpaging.
> 
> What IS the need to send yet another request? It adds just overhead for
> no obvious need. Please show the code that will benefit from the extra
> EVICT_FAIL message.

While in general it's good to keep backward compatibility, I don't think
this interface has ever had a stable, usable release (that didn't
involve the consumer at least carrying hypervisor patches of their own)
so I think it's OK to make fairly large changes in it. 

Tim.

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