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Message-ID: <CAHS8izNuSkxn1HZJ-1W_wa7QsQFE5yKUjbfSgKEzv9tLLOYveQ@mail.gmail.com>
Date: Tue, 28 Oct 2025 09:12:00 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Zi Yan <ziy@...dia.com>
Cc: Byungchul Park <byungchul@...com>, linux-mm@...ck.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, kernel_team@...ynix.com, harry.yoo@...cle.com,
ast@...nel.org, daniel@...earbox.net, davem@...emloft.net, kuba@...nel.org,
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edumazet@...gle.com, pabeni@...hat.com, akpm@...ux-foundation.org,
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dw@...idwei.uk, ap420073@...il.com, dtatulea@...dia.com
Subject: Re: [RFC mm v4 2/2] mm: introduce a new page type for page pool in
page type
On Mon, Oct 27, 2025 at 6:45 PM Zi Yan <ziy@...dia.com> wrote:
>
> On 27 Oct 2025, at 21:28, Mina Almasry wrote:
>
> > 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?
>
> It is done in the hunk below this one:
>
> @@ -1379,9 +1376,12 @@ __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 */
> + 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))
>
> where
> free_pages_prepare()
> -> free_page_is_bad()
> -> page_expected_state()
>
Thanks, looks fine to me then. I'm not extremely familiar with this
code so I won't give a Reviewed-by, but here is an ack, FWIW:
Acked-by: Mina Almasry <almasrymina@...gle.com>
--
Thanks,
Mina
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