Re: [virtio-dev] Re: [PATCH] virtio-balloon: Disable free page hinting/reporting if page poison is disabled

[David Hildenbrand <david@redhat.com>]

 > What do you call "hinting ends" though? The fact we put
> a page in the VQ is not a guarantee that it's been consumed
> by the hypervisor.
> 

I'd say hinting ends once the hypervisor sets FREE_PAGE_REPORT_S_DONE.

> 
> I think a strict definition is this:
> - hint includes a command ID
> - hint implies "page was unused at some point after guest reading command ID"
> 
> 
> Hypervisor can use dirty tracking tricks to get from that to
> "page is unused at the moment".
> 
>> Whereby X is
>> currently assumed to be 0, correct?
> 
> 
> 
> Now we are talking about what's safe to do with the page.
> 
> If POISON flag is set by hypervisor but clear by guest,
> or poison_val is 0, then it's clear it's safe to blow
> away the page if we can figure out it's unused.
> 
> Otherwise, it's much less clear :)

Hah! Agreed :D

> 
> 
> 
> I'll have to come back and re-read the rest next week, this
> is complex stuff and I'm too rushed with other things today.

Yeah, I'm also loaded with other stuff. Maybe Alex has time to
understand the details as well.

-- 
Thanks,

David / dhildenb