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Message-ID: <CAHS8izME4W3ENXNXf4Cxegmk9xnRmKajpRMQ18L0=FGTFebeaw@mail.gmail.com>
Date: Mon, 27 Oct 2025 18:28:09 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Byungchul Park <byungchul@...com>
Cc: linux-mm@...ck.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel_team@...ynix.com, harry.yoo@...cle.com, ast@...nel.org,
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Subject: Re: [RFC mm v4 2/2] mm: introduce a new page type for page pool in
page type
On Thu, Oct 23, 2025 at 12:45 AM Byungchul Park <byungchul@...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@...hat.com>
> Co-developed-by: Pavel Begunkov <asml.silence@...il.com>
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> Signed-off-by: Byungchul Park <byungchul@...com>
> Acked-by: David Hildenbrand <david@...hat.com>
> Acked-by: Zi Yan <ziy@...dia.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?
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