Re: [PATCH net-next v3 1/3] page_pool: Move pp_magic check into helper functions

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

Thanks Toke,

On Wed, 26 Mar 2025 at 10:19, Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Since we are about to stash some more information into the pp_magic
> field, let's move the magic signature checks into a pair of helper
> functions so it can be changed in one place.
>
> Reviewed-by: Mina Almasry <almasrymina@google.com>
> Tested-by: Yonglong Liu <liuyonglong@huawei.com>
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>

Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

> ---
>  drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c |  4 ++--
>  include/net/page_pool/types.h                    | 18 ++++++++++++++++++
>  mm/page_alloc.c                                  |  9 +++------
>  net/core/netmem_priv.h                           |  5 +++++
>  net/core/skbuff.c                                | 16 ++--------------
>  net/core/xdp.c                                   |  4 ++--
>  6 files changed, 32 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> index 6f3094a479e1ec61854bb48a6a0c812167487173..70c6f0b2abb921778c98fbd428594ebd7986a302 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> @@ -706,8 +706,8 @@ 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->pp_magic & ~0x3UL) == PP_SIGNATURE)
> -                                * as we know this is a page_pool page.
> +                               /* No need to check page_pool_page_is_pp() as we
> +                                * know this is a page_pool page.
>                                  */
>                                 page_pool_recycle_direct(page->pp, page);
>                         } while (++n < num);
> diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
> index 36eb57d73abc6cfc601e700ca08be20fb8281055..df0d3c1608929605224feb26173135ff37951ef8 100644
> --- a/include/net/page_pool/types.h
> +++ b/include/net/page_pool/types.h
> @@ -54,6 +54,14 @@ struct pp_alloc_cache {
>         netmem_ref cache[PP_ALLOC_CACHE_SIZE];
>  };
>
> +/* 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.
> + * page_is_pfmemalloc() is checked in __page_pool_put_page() to avoid recycling
> + * the pfmemalloc page.
> + */
> +#define PP_MAGIC_MASK ~0x3UL
> +
>  /**
>   * struct page_pool_params - page pool parameters
>   * @fast:      params accessed frequently on hotpath
> @@ -264,6 +272,11 @@ void page_pool_destroy(struct page_pool *pool);
>  void page_pool_use_xdp_mem(struct page_pool *pool, void (*disconnect)(void *),
>                            const struct xdp_mem_info *mem);
>  void page_pool_put_netmem_bulk(netmem_ref *data, u32 count);
> +
> +static inline bool page_pool_page_is_pp(struct page *page)
> +{
> +       return (page->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE;
> +}
>  #else
>  static inline void page_pool_destroy(struct page_pool *pool)
>  {
> @@ -278,6 +291,11 @@ static inline void page_pool_use_xdp_mem(struct page_pool *pool,
>  static inline void page_pool_put_netmem_bulk(netmem_ref *data, u32 count)
>  {
>  }
> +
> +static inline bool page_pool_page_is_pp(struct page *page)
> +{
> +       return false;
> +}
>  #endif
>
>  void page_pool_put_unrefed_netmem(struct page_pool *pool, netmem_ref netmem,
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 542d25f77be80304b731411ffd29b276ee13be0c..3535ee76afe946cbb042ecbce603bdbedc9233b9 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -55,6 +55,7 @@
>  #include <linux/delayacct.h>
>  #include <linux/cacheinfo.h>
>  #include <linux/pgalloc_tag.h>
> +#include <net/page_pool/types.h>
>  #include <asm/div64.h>
>  #include "internal.h"
>  #include "shuffle.h"
> @@ -872,9 +873,7 @@ static inline bool page_expected_state(struct page *page,
>  #ifdef CONFIG_MEMCG
>                         page->memcg_data |
>  #endif
> -#ifdef CONFIG_PAGE_POOL
> -                       ((page->pp_magic & ~0x3UL) == PP_SIGNATURE) |
> -#endif
> +                       page_pool_page_is_pp(page) |
>                         (page->flags & check_flags)))
>                 return false;
>
> @@ -901,10 +900,8 @@ static const char *page_bad_reason(struct page *page, unsigned long flags)
>         if (unlikely(page->memcg_data))
>                 bad_reason = "page still charged to cgroup";
>  #endif
> -#ifdef CONFIG_PAGE_POOL
> -       if (unlikely((page->pp_magic & ~0x3UL) == PP_SIGNATURE))
> +       if (unlikely(page_pool_page_is_pp(page)))
>                 bad_reason = "page_pool leak";
> -#endif
>         return bad_reason;
>  }
>
> diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h
> index 7eadb8393e002fd1cc2cef8a313d2ea7df76f301..f33162fd281c23e109273ba09950c5d0a2829bc9 100644
> --- a/net/core/netmem_priv.h
> +++ b/net/core/netmem_priv.h
> @@ -18,6 +18,11 @@ static inline void netmem_clear_pp_magic(netmem_ref netmem)
>         __netmem_clear_lsb(netmem)->pp_magic = 0;
>  }
>
> +static inline bool netmem_is_pp(netmem_ref netmem)
> +{
> +       return (netmem_get_pp_magic(netmem) & PP_MAGIC_MASK) == PP_SIGNATURE;
> +}
> +
>  static inline void netmem_set_pp(netmem_ref netmem, struct page_pool *pool)
>  {
>         __netmem_clear_lsb(netmem)->pp = pool;
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index ab8acb737b93299f503e5c298b87e18edd59d555..a64d777488e403d5fdef83ae42ae9e4924c1a0dc 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -893,11 +893,6 @@ static void skb_clone_fraglist(struct sk_buff *skb)
>                 skb_get(list);
>  }
>
> -static bool is_pp_netmem(netmem_ref netmem)
> -{
> -       return (netmem_get_pp_magic(netmem) & ~0x3UL) == PP_SIGNATURE;
> -}
> -
>  int skb_pp_cow_data(struct page_pool *pool, struct sk_buff **pskb,
>                     unsigned int headroom)
>  {
> @@ -995,14 +990,7 @@ bool napi_pp_put_page(netmem_ref netmem)
>  {
>         netmem = netmem_compound_head(netmem);
>
> -       /* page->pp_magic is OR'ed with PP_SIGNATURE after the allocation
> -        * in order to preserve any existing bits, such as bit 0 for the
> -        * head page of compound page and bit 1 for pfmemalloc page, so
> -        * mask those bits for freeing side when doing below checking,
> -        * and page_is_pfmemalloc() is checked in __page_pool_put_page()
> -        * to avoid recycling the pfmemalloc page.
> -        */
> -       if (unlikely(!is_pp_netmem(netmem)))
> +       if (unlikely(!netmem_is_pp(netmem)))
>                 return false;
>
>         page_pool_put_full_netmem(netmem_get_pp(netmem), netmem, false);
> @@ -1042,7 +1030,7 @@ static int skb_pp_frag_ref(struct sk_buff *skb)
>
>         for (i = 0; i < shinfo->nr_frags; i++) {
>                 head_netmem = netmem_compound_head(shinfo->frags[i].netmem);
> -               if (likely(is_pp_netmem(head_netmem)))
> +               if (likely(netmem_is_pp(head_netmem)))
>                         page_pool_ref_netmem(head_netmem);
>                 else
>                         page_ref_inc(netmem_to_page(head_netmem));
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index f86eedad586a77eb63a96a85aa6d068d3e94f077..0ba73943c6eed873b3d1c681b3b9a802b590f2d9 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -437,8 +437,8 @@ void __xdp_return(netmem_ref netmem, enum xdp_mem_type mem_type,
>                 netmem = netmem_compound_head(netmem);
>                 if (napi_direct && xdp_return_frame_no_direct())
>                         napi_direct = false;
> -               /* No need to check ((page->pp_magic & ~0x3UL) == PP_SIGNATURE)
> -                * as mem->type knows this a page_pool page
> +               /* No need to check netmem_is_pp() as mem->type knows this a
> +                * page_pool page
>                  */
>                 page_pool_put_full_netmem(netmem_get_pp(netmem), netmem,
>                                           napi_direct);
>
> --
> 2.48.1
>