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

On Thu, Jul 10, 2025 at 11:29:35AM -0700, Mina Almasry wrote:

On Thu, Jul 10, 2025 at 1:28 AM Byungchul Park [off-list ref] wrote:

quoted

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