Subject: Re: [PATCH v4] mm: introduce a new page type for page pool in page type

From: Lorenzo Stoakes <[email-masked]>
Date: Wed, 13 May 2026 10:42:38 +0100

-cc previous kernel mail address
-cc David's very previous kernel mail address
+cc David's current mail address

Hi,

Just an annoying reminder to please check people's addresses via
get_maintainer.pl, as otherwise stuff might get missed! :)

Cheers, Lorenzo

On Tue, Feb 24, 2026 at 02:13:47PM +0900, Byungchul Park wrote:
> Currently, the condition 'page->pp_magic == PP_SIGNATURE' is used to
> determine if a page belongs to a page pool.  However, with the planned
> removal of @pp_magic, we should instead leverage the page_type in struct
> page, such as PGTY_netpp, for this 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().
>
> Plus, add @page_type to struct net_iov at the same offset as struct page
> so as to use the page_type APIs for struct net_iov as well.  While at it,
> reorder @type and @owner in struct net_iov to avoid a hole and
> increasing the struct size.
>
> This work was inspired by the following link:
>
>   https://lore.kernel.org/all/[email-masked]/
>
> While at it, move the sanity check for page pool to on the free path.
>
> Suggested-by: David Hildenbrand <[email-masked]>
> Co-developed-by: Pavel Begunkov <[email-masked]>
> Signed-off-by: Pavel Begunkov <[email-masked]>
> Signed-off-by: Byungchul Park <[email-masked]>
> Acked-by: David Hildenbrand <[email-masked]>
> Acked-by: Zi Yan <[email-masked]>
> Acked-by: Vlastimil Babka <[email-masked]>
> Reviewed-by: Toke Høiland-Jørgensen <[email-masked]>
> ---
> The following 'Acked-by's were given only for mm part:
>
>   Acked-by: David Hildenbrand <[email-masked]>
>   Acked-by: Zi Yan <[email-masked]>
>   Acked-by: Vlastimil Babka <[email-masked]>
>
> This patch changes both mm and page-pool, but I'm currently targetting
> mm tree because Jakub asked and I also think it's more about mm change.
> See the following link:
>
>   https://lore.kernel.org/all/[email-masked]/
>
> Changes from v3:
> 	1. Rebase on mm-new as of Feb 24, 2026.
> 	2. Fix an issue reported by kernel test robot due to incorrect
> 	   type.
> 	3. Add 'Acked-by: Vlastimil Babka <[email-masked]>'.  Thanks.
>
> Changes from v2:
> 	1. Fix an issue reported by kernel test robot due to incorrect
> 	   type in argument of __netmem_to_page().
>
> Changes from v1:
> 	1. Drop the finalizing patch removing the pp fields of struct
> 	   page since I found that there is still code accessing a pp
> 	   field via struct page.  I will retry the finalizing patch
> 	   after resolving the issue.
> ---
>  .../net/ethernet/mellanox/mlx5/core/en/xdp.c  |  2 +-
>  include/linux/mm.h                            | 27 +++----------------
>  include/linux/page-flags.h                    |  6 +++++
>  include/net/netmem.h                          | 15 +++++++++--
>  mm/page_alloc.c                               | 11 +++++---
>  net/core/netmem_priv.h                        | 23 +++++++---------
>  net/core/page_pool.c                          | 24 +++++++++++++++--
>  7 files changed, 62 insertions(+), 46 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
> index 80f9fc10877ad..7d90d2485c787 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 13336340612e2..0db764b3d6b84 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4824,10 +4824,9 @@ 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.
>   *
> @@ -4862,26 +4861,6 @@ 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 0426cac91c0bb..30c4eb24e4edf 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -939,6 +939,7 @@ enum pagetype {
>  	PGTY_zsmalloc		= 0xf6,
>  	PGTY_unaccepted		= 0xf7,
>  	PGTY_large_kmalloc	= 0xf8,
> +	PGTY_netpp		= 0xf9,
>
>  	PGTY_mapcount_underflow = 0xff
>  };
> @@ -1071,6 +1072,11 @@ PAGE_TYPE_OPS(Zsmalloc, zsmalloc, zsmalloc)
>  PAGE_TYPE_OPS(Unaccepted, unaccepted, unaccepted)
>  PAGE_TYPE_OPS(LargeKmalloc, 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 a96b3e5e5574c..85e3b26ec547f 100644
> --- a/include/net/netmem.h
> +++ b/include/net/netmem.h
> @@ -110,10 +110,21 @@ struct net_iov {
>  			atomic_long_t pp_ref_count;
>  		};
>  	};
> -	struct net_iov_area *owner;
> +
> +	unsigned int page_type;
>  	enum net_iov_type type;
> +	struct net_iov_area *owner;
>  };
>
> +/* Make sure 'the offset of page_type in struct page == the offset of
> + * type in struct net_iov'.
> + */
> +#define NET_IOV_ASSERT_OFFSET(pg, iov)			\
> +	static_assert(offsetof(struct page, pg) ==	\
> +		      offsetof(struct net_iov, iov))
> +NET_IOV_ASSERT_OFFSET(page_type, page_type);
> +#undef NET_IOV_ASSERT_OFFSET
> +
>  struct net_iov_area {
>  	/* Array of net_iovs for this area. */
>  	struct net_iov *niovs;
> @@ -256,7 +267,7 @@ 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 d88c8c67ac0b7..cae9f93271469 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1079,7 +1079,6 @@ static inline bool page_expected_state(struct page *page,
>  #ifdef CONFIG_MEMCG
>  			page->memcg_data |
>  #endif
> -			page_pool_page_is_pp(page) |
>  			(page->flags.f & check_flags)))
>  		return false;
>
> @@ -1106,8 +1105,6 @@ 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
> -	if (unlikely(page_pool_page_is_pp(page)))
> -		bad_reason = "page_pool leak";
>  	return bad_reason;
>  }
>
> @@ -1416,9 +1413,15 @@ __always_inline bool __free_pages_prepare(struct page *page,
>  		mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
>  		folio->mapping = NULL;
>  	}
> -	if (unlikely(page_has_type(page)))
> +	if (unlikely(page_has_type(page))) {
> +		/* networking expects to clear its page type before releasing */
> +		if (unlikely(PageNetpp(page))) {
> +			bad_page(page, "page_pool leak");
> +			return false;
> +		}
>  		/* Reset the page_type (which overlays _mapcount) */
>  		page->page_type = UINT_MAX;
> +	}
>
>  	if (is_check_pages_enabled()) {
>  		if (free_page_is_bad(page))
> diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h
> index 23175cb2bd866..3e6fde8f1726f 100644
> --- a/net/core/netmem_priv.h
> +++ b/net/core/netmem_priv.h
> @@ -8,21 +8,18 @@ static inline unsigned long netmem_get_pp_magic(netmem_ref netmem)
>  	return netmem_to_nmdesc(netmem)->pp_magic & ~PP_DMA_INDEX_MASK;
>  }
>
> -static inline void netmem_or_pp_magic(netmem_ref netmem, unsigned long pp_magic)
> -{
> -	netmem_to_nmdesc(netmem)->pp_magic |= pp_magic;
> -}
> -
> -static inline void netmem_clear_pp_magic(netmem_ref netmem)
> -{
> -	WARN_ON_ONCE(netmem_to_nmdesc(netmem)->pp_magic & PP_DMA_INDEX_MASK);
> -
> -	netmem_to_nmdesc(netmem)->pp_magic = 0;
> -}
> -
>  static inline bool netmem_is_pp(netmem_ref netmem)
>  {
> -	return (netmem_get_pp_magic(netmem) & PP_MAGIC_MASK) == PP_SIGNATURE;
> +	struct page *page;
> +
> +	/* XXX: Now that the offset of page_type is shared between
> +	 * struct page and net_iov, just cast the netmem to struct page
> +	 * unconditionally by clearing NET_IOV if any, no matter whether
> +	 * it comes from struct net_iov or struct page.  This should be
> +	 * adjusted once the offset is no longer shared.
> +	 */
> +	page = (struct page *)((__force unsigned long)netmem & ~NET_IOV);
> +	return PageNetpp(page);
>  }
>
>  static inline void netmem_set_pp(netmem_ref netmem, struct page_pool *pool)
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 265a729431bb7..877bbf7a19389 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -702,8 +702,18 @@ s32 page_pool_inflight(const struct page_pool *pool, bool strict)
>
>  void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
>  {
> +	struct page *page;
> +
>  	netmem_set_pp(netmem, pool);
> -	netmem_or_pp_magic(netmem, PP_SIGNATURE);
> +
> +	/* XXX: Now that the offset of page_type is shared between
> +	 * struct page and net_iov, just cast the netmem to struct page
> +	 * unconditionally by clearing NET_IOV if any, no matter whether
> +	 * it comes from struct net_iov or struct page.  This should be
> +	 * adjusted once the offset is no longer shared.
> +	 */
> +	page = (struct page *)((__force unsigned long)netmem & ~NET_IOV);
> +	__SetPageNetpp(page);
>
>  	/* Ensuring all pages have been split into one fragment initially:
>  	 * page_pool_set_pp_info() is only called once for every page when it
> @@ -718,7 +728,17 @@ void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
>
>  void page_pool_clear_pp_info(netmem_ref netmem)
>  {
> -	netmem_clear_pp_magic(netmem);
> +	struct page *page;
> +
> +	/* XXX: Now that the offset of page_type is shared between
> +	 * struct page and net_iov, just cast the netmem to struct page
> +	 * unconditionally by clearing NET_IOV if any, no matter whether
> +	 * it comes from struct net_iov or struct page.  This should be
> +	 * adjusted once the offset is no longer shared.
> +	 */
> +	page = (struct page *)((__force unsigned long)netmem & ~NET_IOV);
> +	__ClearPageNetpp(page);
> +
>  	netmem_set_pp(netmem, NULL);
>  }
>
> --
> 2.17.1
>