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Message-ID: <951BA2D7-E220-4F41-BE16-C4C10318A627@nvidia.com>
Date: Tue, 29 Jul 2025 10:20:22 -0400
From: Zi Yan <ziy@...dia.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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sfr@...b.auug.org.au
Subject: Re: [PATCH linux-next v3] mm, page_pool: introduce a new page type
for page pool in page type
On 29 Jul 2025, at 7:02, Byungchul Park wrote:
> Changes from v2:
> 1. Rebase on linux-next as of Jul 29.
> 2. Skip 'niov->pp = NULL' when it's allocated using __GFP_ZERO.
> 3. Change trivial coding style. (feedbacked by Mina)
> 4. Add Co-developed-by, Acked-by, and Reviewed-by properly.
> Thanks to all.
>
> Changes from v1:
> 1. Rebase on linux-next.
> 2. Initialize net_iov->pp = NULL when allocating net_iov in
> net_devmem_bind_dmabuf() and io_zcrx_create_area().
> 3. Use ->pp for net_iov to identify if it's pp rather than
> always consider net_iov as pp.
> 4. Add Suggested-by: David Hildenbrand <david@...hat.com>.
>
> ---8<---
> From 88bcb9907a0cef65a9c0adf35e144f9eb67e0542 Mon Sep 17 00:00:00 2001
> From: Byungchul Park <byungchul@...com>
> Date: Tue, 29 Jul 2025 19:49:44 +0900
> Subject: [PATCH linux-next v3] mm, page_pool: introduce a new page type for page pool in page type
>
> ->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().
>
> For net_iov, use ->pp to identify if it's pp, with making sure that ->pp
> is NULL for non-pp net_iov.
>
> 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>
> Reviewed-by: Mina Almasry <almasrymina@...gle.com>
> ---
> .../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 +-
> io_uring/zcrx.c | 4 +++
> mm/page_alloc.c | 7 +++--
> net/core/devmem.c | 1 +
> net/core/netmem_priv.h | 23 +++++++---------
> net/core/page_pool.c | 10 +++++--
> 9 files changed, 37 insertions(+), 45 deletions(-)
>
<snip>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 0d4ee569aa6b..d01b296e7184 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4171,10 +4171,9 @@ 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.
> *
> @@ -4205,26 +4204,6 @@ 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 8d3fa3a91ce4..84247e39e9e7 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -933,6 +933,7 @@ enum pagetype {
> PGTY_zsmalloc = 0xf6,
> PGTY_unaccepted = 0xf7,
> PGTY_large_kmalloc = 0xf8,
> + PGTY_netpp = 0xf9,
>
> PGTY_mapcount_underflow = 0xff
> };
> @@ -1077,6 +1078,11 @@ 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.
<snip>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d1d037f97c5f..2f6a55fab942 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) |
> (page->flags & check_flags)))
> return false;
>
> @@ -1069,8 +1068,6 @@ 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;
> }
>
> @@ -1379,9 +1376,11 @@ __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))) {
> + WARN_ON_ONCE(PageNetpp(page));
> /* Reset the page_type (which overlays _mapcount) */
> page->page_type = UINT_MAX;
> + }
>
> if (is_check_pages_enabled()) {
> if (free_page_is_bad(page))
The mm part looks good to me.
Acked-by: Zi Yan <ziy@...dia.com>
Best Regards,
Yan, Zi
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