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

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Apr 17, 2020 at 12:31:14PM +0200, David Hildenbrand wrote:
> On 17.04.20 12:29, Michael S. Tsirkin wrote:
> > On Fri, Apr 17, 2020 at 12:26:24PM +0200, David Hildenbrand wrote:
> >> On 17.04.20 12:19, Michael S. Tsirkin wrote:
> >>> On Fri, Apr 17, 2020 at 12:09:38PM +0200, David Hildenbrand wrote:
> >>>>  > 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.
> >>>
> >>> Can't find that one anywhere. what did I miss?
> >>
> >> Sorry, the QEMU implementation is confusing. FREE_PAGE_REPORT_S_DONE is
> >> translated to VIRTIO_BALLOON_CMD_ID_DONE
> > 
> > Well VIRTIO_BALLOON_CMD_ID_DONE just means "don't give me any
> > more hints, I finished migration".
> > Guest will stop hinting even without that once it scans all
> > free memory.
> 
> Yeah, that's the end of the whole process where you can be sure the host
> processed all requests definetly.

It's not guaranteed to happen :) Sending an interrupt at the end
of each scan doubles the overhead ...

> -- 
> Thanks,
> 
> David / dhildenb