Re: [PATCH v4 3/3] multifd: Implement zerocopy write in multifd migration (multifd-zerocopy)

[Leonardo Bras Soares Passos <leobras@redhat.com>]

On Wed, Oct 13, 2021 at 3:24 AM Peter Xu <peterx@redhat.com> wrote:
>
> On Sat, Oct 09, 2021 at 04:56:13AM -0300, Leonardo Bras wrote:
> > diff --git a/qapi/migration.json b/qapi/migration.json
> > index 88f07baedd..c4890cbb54 100644
> > --- a/qapi/migration.json
> > +++ b/qapi/migration.json
> > @@ -724,6 +724,11 @@
> >  #                      will consume more CPU.
> >  #                      Defaults to 1. (Since 5.0)
> >  #
> > +# @multifd-zerocopy: Controls behavior on sending memory pages on multifd migration.
> > +#                    When true, enables a zerocopy mechanism for sending memory
> > +#                    pages, if host does support it.
> > +#                    Defaults to false. (Since 6.2)
> > +#
>
> Shall we keep it named "@zerocopy"?  Yes we have that dependency with multifd,
> but it's fine to just fail the configuration if multifd not set. The thing is
> we don't know whether that dependency will last forever, and we probably don't
> want to introduce yet another feature bit when we can remove the dependency..
> as we can't remove the old one to be compatible.

It makes sense not wanting to create a new future bit in the future,
but if we just add a
"@zerocopy' , wouldn't we need to fail every migration setup that
don't support zerocopy?

(Thinking back, to stay as it is, it would also be necessary that I
find a way to fail other multifd setups that don't support zerocopy,
for v5)

>
> --
> Peter Xu
>