Re: [PATCH v10 00/37] mm/virtio: skip redundant zeroing of host-zeroed pages

[Lorenzo Stoakes <ljs@kernel.org>]

On Mon, Jun 08, 2026 at 10:17:47AM +0100, Lorenzo Stoakes wrote:
> On Mon, Jun 08, 2026 at 04:33:46AM -0400, Michael S. Tsirkin wrote:
> > Further, on architectures with aliasing caches, upstream with init_on_alloc
> > double-zeros user pages: once via kernel_init_pages() in
> > post_alloc_hook, and again via clear_user_highpage() at the
> > callsite (because user_alloc_needs_zeroing() returns true).
> > This series eliminates that double-zeroing by moving the zeroing
> > into the post_alloc_hook + propagating the "host
> > already zeroed this page" information through the buddy allocator.
> >
> > For page reporting, VIRTIO_BALLOON_F_DEVICE_INIT_REPORTED (bit 6)
> > is used. For the inflate/deflate path,
> > VIRTIO_BALLOON_F_DEVICE_INIT_ON_INFLATE (bit 7) is used.
> >
> > Virtio spec: https://lore.kernel.org/all/cover.1778140241.git.mst@redhat.com
> >
> > Based on v7.1-rc6.  When applying on mm-unstable, two conflicts
> > are expected:
> > - kernel_init_pages() was renamed to clear_highpages_kasan_tagged()
> >   in mm-unstable.  Use clear_highpages_kasan_tagged() in the
> >   post_alloc_hook else branch.
> > - FPI_PREPARED uses BIT(3) in mm-unstable.  Bump FPI_ZEROED to
> >   BIT(4).
> > Build-tested on mm-unstable at e9dd96806dbc:
> > https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git zero-mm-unstable
> >
> > Patches 1-5: fixes/cleanups, dependencies of the zeroing patches.
> > Patches 6-9: thread user_addr through page allocator, contig API,
> >   and gigantic hugetlb allocation.
> > Patches 10-16: folio_zero_user in post_alloc_hook, vma_alloc_zeroed
> >   conversion, raw fault address threading.
> > Patches 17-24: PG_zeroed flag, aliasing guard, buddy merge/split
> >   tracking, FPI_ZEROED optimization, folio_put_zeroed.
> > Patches 25-27: __GFP_ZERO callsite conversions (alloc_anon_folio,
> >   vma_alloc_anon_folio_pmd) with memcg charge failure mitigation.
> > Patches 28-29: hugetlb __GFP_ZERO + HPG_zeroed.
> > Patches 30-35: page reporting zeroing (DEVICE_INIT_REPORTED),
> >   disable indirect descriptors.
> > Patches 36-37: inflate/deflate zeroing (DEVICE_INIT_ON_INFLATE).
>
> This seems far too much for one series.
>
> YOu're doing a bunch of mm stuff that seems relatively independent, then
> putting the virtio stuff on top.
>
> I think this should be broken out into separate series laying foundations
> rather than doing it all in one go, which is also difficult for review
> purposes.
>
> Adding a new folio flag is contentious also for instance, we maybe want to
> go bit-by-bit and ensure that each foundational element is acceptable
> before doing the next bit rather than having it as part of a big series.
>
> Looking through the changelog only adds to this feeling! Huge numbers of
> changes, even relatively recently and I'm not sure all relevant maintainers
> in mm have had a look through either.
>
> Thanks, Lorenzo

Additionally, it seems you've missed/ignored (I hope not) a bunch of
pre-existing feedback, so it'd be helpful if you'd carefully go through
what people have previously asked!

Keeping track of that, especially on a big series, is a lot of work.

Thanks, Lorenzo