Subject: Re: [RESEND PATCH net-next] netmem: remove the pp fields from net_iov

From: Byungchul Park <[email-masked]>
Date: Thu, 26 Feb 2026 09:21:27 +0900

On Wed, Feb 25, 2026 at 09:57:17AM -0800, Mina Almasry wrote:
> On Mon, Feb 23, 2026 at 10:14 PM Byungchul Park <[email-masked]> wrote:
> >
> > Now that the pp fields in net_iov have no users, remove them from
> > net_iov and clean up.
> >
> > Signed-off-by: Byungchul Park <[email-masked]>
> > ---
> > The original post was:
> >
> >   https://lore.kernel.org/all/[email-masked]/
> >
> > 1/3 was covered by Pavel's patch:
> >
> >   commit f0243d2b86b97 ("io_uring/zcrx: convert to use netmem_desc").
> >
> > 2/3 was taken by Jakub and merged:
> >
> >   commit df59bb5b9af3f ("netmem, devmem, tcp: access pp fields through
> >   @desc in net_iov")
> >
> > Now that io-uring and net core changes converge in one tree, I'm
> > resending the 3/3, which is what Jakub asked:
> >
> >   https://lore.kernel.org/all/[email-masked]/
> > ---
> >  include/net/netmem.h | 38 +-------------------------------------
> >  1 file changed, 1 insertion(+), 37 deletions(-)
> >
> > diff --git a/include/net/netmem.h b/include/net/netmem.h
> > index a96b3e5e5574..a6d65ced5231 100644
> > --- a/include/net/netmem.h
> > +++ b/include/net/netmem.h
> > @@ -93,23 +93,7 @@ enum net_iov_type {
> >   *             supported.
> >   */
> >  struct net_iov {
> > -       union {
> > -               struct netmem_desc desc;
> > -
> > -               /* XXX: The following part should be removed once all
> > -                * the references to them are converted so as to be
> > -                * accessed via netmem_desc e.g. niov->desc.pp instead
> > -                * of niov->pp.
> > -                */
> > -               struct {
> > -                       unsigned long _flags;
> > -                       unsigned long pp_magic;
> > -                       struct page_pool *pp;
> > -                       unsigned long _pp_mapping_pad;
> > -                       unsigned long dma_addr;
> > -                       atomic_long_t pp_ref_count;
> > -               };
> > -       };
> > +       struct netmem_desc desc;
> >         struct net_iov_area *owner;
> >         enum net_iov_type type;
> >  };
> > @@ -123,26 +107,6 @@ struct net_iov_area {
> >         unsigned long base_virtual;
> >  };
> >
> > -/* net_iov is union'ed with struct netmem_desc mirroring struct page, so
> > - * the page_pool can access these fields without worrying whether the
> > - * underlying fields are accessed via netmem_desc or directly via
> > - * net_iov, until all the references to them are converted so as to be
> > - * accessed via netmem_desc e.g. niov->desc.pp instead of niov->pp.
> > - *
> > - * The non-net stack fields of struct page are private to the mm stack
> > - * and must never be mirrored to net_iov.
> > - */
> > -#define NET_IOV_ASSERT_OFFSET(desc, iov)                    \
> > -       static_assert(offsetof(struct netmem_desc, desc) == \
> > -                     offsetof(struct net_iov, iov))
> > -NET_IOV_ASSERT_OFFSET(_flags, _flags);
> > -NET_IOV_ASSERT_OFFSET(pp_magic, pp_magic);
> > -NET_IOV_ASSERT_OFFSET(pp, pp);
> > -NET_IOV_ASSERT_OFFSET(_pp_mapping_pad, _pp_mapping_pad);
> > -NET_IOV_ASSERT_OFFSET(dma_addr, dma_addr);
> > -NET_IOV_ASSERT_OFFSET(pp_ref_count, pp_ref_count);
> > -#undef NET_IOV_ASSERT_OFFSET
> > -
> 
> Probably better to retain an assert that netmem_desc is the first
> field in struct net_iov, no?

What is the assert for?  Can you give an example that might lead wrong
without the assert?

	Byungchul

> There technically is no assert that netmem_desc is the first field of
> struct page, but it's generally well understood that the memory
> descriptor types should be the first field of struct page. It's not
> well understand that the netmem_desc type should be the first field in
> struct net_iov though.
> 
> --
> Thanks,
> Mina