Re: [PATCH RFC v2 00/18] mm/virtio: skip redundant zeroing of host-zeroed reported pages

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

On Tue, Apr 21, 2026 at 12:51:00PM -0400, Gregory Price wrote:
> On Tue, Apr 21, 2026 at 09:06:00AM -0400, Michael S. Tsirkin wrote:
> > On Mon, Apr 20, 2026 at 10:38:19PM -0400, Gregory Price wrote:
> > > 
> > > Can we leave folio_zero_user() callers the same, but add a PG_zeroed
> > > check in folio_zero_user() that skips the zeroing (but not the cache
> > > flush) and clear the PG_zeroed bit?
> > > 
> > > Is this feasible?
> > 
> > I do not see how - this would require leaking the page flag out of the
> > buddy allocator.
> >
> 
> Right, but you're leaking that bit of information out one way or another
> - whether it's a page-flag or something else (pghint_t) you have the
> same lifecycle problems (when does it become invalidated? how long can
> it be trusted for?).
>
> I suppose at least with (pghint_t) the data (in theory) falls out of
> scope and doesn't live with the page - but guaranteed it just ends up
> polluting more and more interfaces.
> 
> I'm seeing why David's suggest to plumb __GFP_ZERO correctly makes
> sense, it's really the only feasible approach here that doesn't generate
> a staleness problem with whatever information you try to leak out.
> 
> ~Gregory

OK, v3 with that incoming.