Re: [PATCH net-next v9 6/8] mlx4: use netmem descriptor and APIs for page pool

[Byungchul Park <byungchul@sk.com>]

On Thu, Jul 10, 2025 at 11:29:35AM -0700, Mina Almasry wrote:
> On Thu, Jul 10, 2025 at 1:28 AM Byungchul Park <byungchul@sk.com> wrote:
> >
> > To simplify struct page, the effort to separate its own descriptor from
> > struct page is required and the work for page pool is on going.
> >
> > Use netmem descriptor and APIs for page pool in mlx4 code.
> >
> > Signed-off-by: Byungchul Park <byungchul@sk.com>
> > ---
> >  drivers/net/ethernet/mellanox/mlx4/en_rx.c   | 48 +++++++++++---------
> >  drivers/net/ethernet/mellanox/mlx4/en_tx.c   |  8 ++--
> >  drivers/net/ethernet/mellanox/mlx4/mlx4_en.h |  4 +-
> >  3 files changed, 32 insertions(+), 28 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> > index b33285d755b9..7cf0d2dc5011 100644
> > --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> > +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> > @@ -62,18 +62,18 @@ static int mlx4_en_alloc_frags(struct mlx4_en_priv *priv,
> >         int i;
> >
> >         for (i = 0; i < priv->num_frags; i++, frags++) {
> > -               if (!frags->page) {
> > -                       frags->page = page_pool_alloc_pages(ring->pp, gfp);
> > -                       if (!frags->page) {
> > +               if (!frags->netmem) {
> > +                       frags->netmem = page_pool_alloc_netmems(ring->pp, gfp);
> > +                       if (!frags->netmem) {
> >                                 ring->alloc_fail++;
> >                                 return -ENOMEM;
> >                         }
> > -                       page_pool_fragment_page(frags->page, 1);
> > +                       page_pool_fragment_netmem(frags->netmem, 1);
> >                         frags->page_offset = priv->rx_headroom;
> >
> >                         ring->rx_alloc_pages++;
> >                 }
> > -               dma = page_pool_get_dma_addr(frags->page);
> > +               dma = page_pool_get_dma_addr_netmem(frags->netmem);
> >                 rx_desc->data[i].addr = cpu_to_be64(dma + frags->page_offset);
> >         }
> >         return 0;
> > @@ -83,10 +83,10 @@ static void mlx4_en_free_frag(const struct mlx4_en_priv *priv,
> >                               struct mlx4_en_rx_ring *ring,
> >                               struct mlx4_en_rx_alloc *frag)
> >  {
> > -       if (frag->page)
> > -               page_pool_put_full_page(ring->pp, frag->page, false);
> > +       if (frag->netmem)
> > +               page_pool_put_full_netmem(ring->pp, frag->netmem, false);
> >         /* We need to clear all fields, otherwise a change of priv->log_rx_info
> > -        * could lead to see garbage later in frag->page.
> > +        * could lead to see garbage later in frag->netmem.
> >          */
> >         memset(frag, 0, sizeof(*frag));
> >  }
> > @@ -440,29 +440,33 @@ static int mlx4_en_complete_rx_desc(struct mlx4_en_priv *priv,
> >         unsigned int truesize = 0;
> >         bool release = true;
> >         int nr, frag_size;
> > -       struct page *page;
> > +       netmem_ref netmem;
> >         dma_addr_t dma;
> >
> >         /* Collect used fragments while replacing them in the HW descriptors */
> >         for (nr = 0;; frags++) {
> >                 frag_size = min_t(int, length, frag_info->frag_size);
> >
> > -               page = frags->page;
> > -               if (unlikely(!page))
> > +               netmem = frags->netmem;
> > +               if (unlikely(!netmem))
> >                         goto fail;
> >
> > -               dma = page_pool_get_dma_addr(page);
> > +               dma = page_pool_get_dma_addr_netmem(netmem);
> >                 dma_sync_single_range_for_cpu(priv->ddev, dma, frags->page_offset,
> >                                               frag_size, priv->dma_dir);
> >
> > -               __skb_fill_page_desc(skb, nr, page, frags->page_offset,
> > -                                    frag_size);
> > +               __skb_fill_netmem_desc(skb, nr, netmem, frags->page_offset,
> > +                                      frag_size);
> >
> >                 truesize += frag_info->frag_stride;
> >                 if (frag_info->frag_stride == PAGE_SIZE / 2) {
> > +                       struct page *page = netmem_to_page(netmem);
> 
> This cast is not safe, try to use the netmem type directly.

Can it be net_iov?  It already ensures it's a page-backed netmem.  Why
is that unsafe?

With netmem, page_count() and page_to_nid() cannot be used, but needed.
Or checking 'page == NULL' after the casting works for you?

	Byungchul

> --
> Thanks,
> Mina