Re: [Xen-devel] [PATCH-for-4.13] x86/mm: don't needlessly veto migration

[Jan Beulich <jbeulich@xxxxxxxx>]

On 01.10.2019 12:40, Paul Durrant wrote:
>> From: George Dunlap <george.dunlap@xxxxxxxxxx>
>> Sent: 01 October 2019 11:34
>>
>> One thing we could imagine is that when specific devices have an active
>> emulator (or whatever) propagating the dirty information, for that code
>> to tell Xen, "I am implementing dirty tracking for this device".  Then
>> when the toolstack enables logdirty, the check can be, "Are there any
>> devices *that don't have external dirty tracking enabled* assigned to
>> the guest?"
> 
> And what about existing emulators setting pages dirty at the moment? I
> don't see why Xen's internal dirty page logging is considered definitive
> because AFAICT that is really not the case even now.

I don't think external emulators already setting pages dirty matter here.
All they want/need to do is advertise which device(s) they take care of.
These emulators actually _help_ Xen maintain a correct picture. What your
patch imo does though is (further) weaken the current model.

Jan

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