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Message-ID: <64E18E02-727B-47C4-8849-486AB98CACD8@nvidia.com>
Date: Mon, 27 Oct 2025 21:45:15 -0400
From: Zi Yan <ziy@...dia.com>
To: Mina Almasry <almasrymina@...gle.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, hawk@...nel.org,
john.fastabend@...il.com, sdf@...ichev.me, saeedm@...dia.com,
leon@...nel.org, tariqt@...dia.com, mbloch@...dia.com, andrew+netdev@...n.ch,
edumazet@...gle.com, pabeni@...hat.com, akpm@...ux-foundation.org,
david@...hat.com, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com,
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kas@...nel.org, yuzhao@...gle.com, usamaarif642@...il.com,
baolin.wang@...ux.alibaba.com, toke@...hat.com, asml.silence@...il.com,
bpf@...r.kernel.org, linux-rdma@...r.kernel.org, sfr@...b.auug.org.au,
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 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()
--
Best Regards,
Yan, Zi
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