Re: [virtio-comment] [PATCH v3 2/3] content: Document balloon feature page poison

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 26 May 2020 20:20:21 -0700
Alexander Duyck <alexander.duyck@gmail.com> wrote:

> On Tue, May 26, 2020 at 8:38 AM Cornelia Huck <cohuck@redhat.com> wrote:
> >
> > On Tue, 26 May 2020 17:28:00 +0200
> > David Hildenbrand <david@redhat.com> wrote:
> >  
> > > On 26.05.20 16:50, Alexander Duyck wrote:  
> > > > On Tue, May 26, 2020 at 1:24 AM David Hildenbrand <david@redhat.com> wrote:  
> >  
> > > >> Still wondering what to do with free page hinting ... in the meantime
> > > >> I'll have a look at free page reporting :)  
> > > >
> > > > The problem is it is already out there so I worry we wouldn't ever be
> > > > able to get rid of it. At most we could deprecate it, but we are still
> > > > stuck with it consuming bit resources and such.  
> > >
> > > Yeah, that's not an issue, they will simply turn to dead bits with
> > > minimal documentation. I just don't see us fixing/supporting that
> > > feature, really. Let's see what @MST things when he has time to look
> > > into this.
> > >  
> >
> > If free page hinting is broken enough that we don't want anybody to try
> > implementing it, we maybe could:
> >
> > - reserve the feature bit,
> > - say that the device SHOULD NOT offer it,
> > - say that the driver SHOULD NOT accept it?
> >
> > Would avoid conflicts, and tell implementors that they should not
> > bother. (We can then proceed to start deprecating the Linux/QEMU
> > implementations.)  
> 
> What I might do is just try to work around it for now. I might
> re-order my patches so that I can push the page poison and free page
> reporting bits with the free page hinting changes at the end of the
> set. That way if we decide to take a different route then we can
> always go back and change that later and it won't have an impact on
> the earlier changes.

Maybe:
- only add the hinting feature bit as reserved,
- document page poison and free page reporting,
- and then think about what to do with the hinting?

Just to make it clear that there is another feature bit out there; but
maybe that is overkill and we should just go ahead with patches 2/3 for
now.