Re: [RFC mm v4 2/2] mm: introduce a new page type for page pool in page type

[Mina Almasry <almasrymina@google.com>]

On Thu, Oct 23, 2025 at 12:45 AM Byungchul Park <byungchul@sk.com> wrote:
>
> ->pp_magic field in struct page is current used to identify if a page
> belongs to a page pool.  However, ->pp_magic will be removed and page
> type bit in struct page e.i. PGTY_netpp can be used for that purpose.
>
> Introduce and use the page type APIs e.g. PageNetpp(), __SetPageNetpp(),
> and __ClearPageNetpp() instead, and remove the existing APIs accessing
> ->pp_magic e.g. page_pool_page_is_pp(), netmem_or_pp_magic(), and
> netmem_clear_pp_magic().
>
> This work was inspired by the following link:
>
> [1] https://lore.kernel.org/all/582f41c0-2742-4400-9c81-0d46bf4e8314@gmail.com/
>
> While at it, move the sanity check for page pool to on free.
>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Co-developed-by: Pavel Begunkov <asml.silence@gmail.com>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> Signed-off-by: Byungchul Park <byungchul@sk.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Acked-by: Zi Yan <ziy@nvidia.com>
> ---
> Hi Mina,
>
> I dropped your Reviewed-by tag since there are updates on some comments
> in network part.  Can I still keep your Reviewed-by?
>
>         Byungchul
> ---
>  .../net/ethernet/mellanox/mlx5/core/en/xdp.c  |  2 +-
>  include/linux/mm.h                            | 27 +++----------------
>  include/linux/page-flags.h                    |  6 +++++
>  include/net/netmem.h                          |  2 +-
>  mm/page_alloc.c                               |  8 +++---
>  net/core/netmem_priv.h                        | 17 +++---------
>  net/core/page_pool.c                          | 14 +++++-----
>  7 files changed, 25 insertions(+), 51 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> index 5d51600935a6..def274f5c1ca 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> @@ -707,7 +707,7 @@ static void mlx5e_free_xdpsq_desc(struct mlx5e_xdpsq *sq,
>                                 xdpi = mlx5e_xdpi_fifo_pop(xdpi_fifo);
>                                 page = xdpi.page.page;
>
> -                               /* No need to check page_pool_page_is_pp() as we
> +                               /* No need to check PageNetpp() as we
>                                  * know this is a page_pool page.
>                                  */
>                                 page_pool_recycle_direct(pp_page_to_nmdesc(page)->pp,
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index b6fdf3557807..f5155f1c75f5 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4361,10 +4361,9 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
>   * DMA mapping IDs for page_pool
>   *
>   * When DMA-mapping a page, page_pool allocates an ID (from an xarray) and
> - * stashes it in the upper bits of page->pp_magic. We always want to be able to
> - * unambiguously identify page pool pages (using page_pool_page_is_pp()). Non-PP
> - * pages can have arbitrary kernel pointers stored in the same field as pp_magic
> - * (since it overlaps with page->lru.next), so we must ensure that we cannot
> + * stashes it in the upper bits of page->pp_magic. Non-PP pages can have
> + * arbitrary kernel pointers stored in the same field as pp_magic (since
> + * it overlaps with page->lru.next), so we must ensure that we cannot
>   * mistake a valid kernel pointer with any of the values we write into this
>   * field.
>   *
> @@ -4399,26 +4398,6 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
>  #define PP_DMA_INDEX_MASK GENMASK(PP_DMA_INDEX_BITS + PP_DMA_INDEX_SHIFT - 1, \
>                                   PP_DMA_INDEX_SHIFT)
>
> -/* Mask used for checking in page_pool_page_is_pp() below. page->pp_magic is
> - * OR'ed with PP_SIGNATURE after the allocation in order to preserve bit 0 for
> - * the head page of compound page and bit 1 for pfmemalloc page, as well as the
> - * bits used for the DMA index. page_is_pfmemalloc() is checked in
> - * __page_pool_put_page() to avoid recycling the pfmemalloc page.
> - */
> -#define PP_MAGIC_MASK ~(PP_DMA_INDEX_MASK | 0x3UL)
> -
> -#ifdef CONFIG_PAGE_POOL
> -static inline bool page_pool_page_is_pp(const struct page *page)
> -{
> -       return (page->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE;
> -}
> -#else
> -static inline bool page_pool_page_is_pp(const struct page *page)
> -{
> -       return false;
> -}
> -#endif
> -
>  #define PAGE_SNAPSHOT_FAITHFUL (1 << 0)
>  #define PAGE_SNAPSHOT_PG_BUDDY (1 << 1)
>  #define PAGE_SNAPSHOT_PG_IDLE  (1 << 2)
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 0091ad1986bf..edf5418c91dd 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -934,6 +934,7 @@ enum pagetype {
>         PGTY_zsmalloc           = 0xf6,
>         PGTY_unaccepted         = 0xf7,
>         PGTY_large_kmalloc      = 0xf8,
> +       PGTY_netpp              = 0xf9,
>
>         PGTY_mapcount_underflow = 0xff
>  };
> @@ -1078,6 +1079,11 @@ PAGE_TYPE_OPS(Zsmalloc, zsmalloc, zsmalloc)
>  PAGE_TYPE_OPS(Unaccepted, unaccepted, unaccepted)
>  FOLIO_TYPE_OPS(large_kmalloc, large_kmalloc)
>
> +/*
> + * Marks page_pool allocated pages.
> + */
> +PAGE_TYPE_OPS(Netpp, netpp, netpp)
> +
>  /**
>   * PageHuge - Determine if the page belongs to hugetlbfs
>   * @page: The page to test.
> diff --git a/include/net/netmem.h b/include/net/netmem.h
> index 651e2c62d1dd..0ec4c7561081 100644
> --- a/include/net/netmem.h
> +++ b/include/net/netmem.h
> @@ -260,7 +260,7 @@ static inline unsigned long netmem_pfn_trace(netmem_ref netmem)
>   */
>  #define pp_page_to_nmdesc(p)                                           \
>  ({                                                                     \
> -       DEBUG_NET_WARN_ON_ONCE(!page_pool_page_is_pp(p));               \
> +       DEBUG_NET_WARN_ON_ONCE(!PageNetpp(p));                          \
>         __pp_page_to_nmdesc(p);                                         \
>  })
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index fb91c566327c..c69ed3741bbc 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1042,7 +1042,6 @@ static inline bool page_expected_state(struct page *page,
>  #ifdef CONFIG_MEMCG
>                         page->memcg_data |
>  #endif
> -                       page_pool_page_is_pp(page) |

Shouldn't you replace the page_pool_page_is_pp check with a PageNetpp
check in this call site and below? Or is that no longer necessary for
some reason?