[RFC mm v4 0/2] mm, page_pool: introduce a new page type for page pool in page type

[RFC mm v4 0/2] mm, page_pool: introduce a new page type for page pool in page type

[Byungchul Park]

This patch is supposed to go via the mm tree, but it currently also
depends on patches in the net-next tree.  For now, this patch is based
on linux-next, but will apply cleanly (or get rebased) after mm tree was
rebased.

Changes from v3:
	1. Rebase on next-20251023 of linux-next.
	2. Split into two, mm changes and network changes.
	3. Improve the comments (feedbacked by Jakub)

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@redhat.com>.

Byungchul Park (2):
  page_pool: check if nmdesc->pp is !NULL to confirm its usage as pp for
    net_iov
  mm: introduce a new page type for page pool in page type

 .../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/devmem.c                             |  1 +
 net/core/netmem_priv.h                        | 25 +++++++++--------
 net/core/page_pool.c                          | 14 ++++++++--
 8 files changed, 40 insertions(+), 45 deletions(-)


base-commit: efb26a23ed5f5dc3554886ab398f559dcb1de96b
-- 
2.17.1

[RFC mm v4 1/2] page_pool: check if nmdesc->pp is !NULL to confirm its usage as pp for net_iov

[Byungchul Park]

->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.g. PGTY_netpp should be used for that purpose.

As a preparation, the check for net_iov, that is not page-backed, should
avoid using ->pp_magic since net_iov doens't have to do with page type.
Instead, nmdesc->pp can be used if a net_iov or its nmdesc belongs to a
page pool, by making sure nmdesc->pp is NULL otherwise.

For page-backed netmem, just leave unchanged as is, while for net_iov,
make sure nmdesc->pp is initialized to NULL and use nmdesc->pp for the
check.

Signed-off-by: Byungchul Park <byungchul@sk.com>
---
 net/core/devmem.c      |  1 +
 net/core/netmem_priv.h |  8 ++++++++
 net/core/page_pool.c   | 16 ++++++++++++++--
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/net/core/devmem.c b/net/core/devmem.c
index d9de31a6cc7f..f81b700f1fd1 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -291,6 +291,7 @@ net_devmem_bind_dmabuf(struct net_device *dev,
 			niov = &owner->area.niovs[i];
 			niov->type = NET_IOV_DMABUF;
 			niov->owner = &owner->area;
+			niov->desc.pp = NULL;
 			page_pool_set_dma_addr_netmem(net_iov_to_netmem(niov),
 						      net_devmem_get_dma_addr(niov));
 			if (direction == DMA_TO_DEVICE)
diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h
index 23175cb2bd86..5561fd556bc5 100644
--- a/net/core/netmem_priv.h
+++ b/net/core/netmem_priv.h
@@ -22,6 +22,14 @@ static inline void netmem_clear_pp_magic(netmem_ref netmem)
 
 static inline bool netmem_is_pp(netmem_ref netmem)
 {
+	/* net_iov may be part of a page pool.  For net_iov, ->pp in
+	 * net_iov.desc can be used to determine if the pages belong to
+	 * a page pool.  Ensure that the ->pp either points to its page
+	 * pool or is set to NULL if it does not.
+	 */
+	if (netmem_is_net_iov(netmem))
+		return !!netmem_to_nmdesc(netmem)->pp;
+
 	return (netmem_get_pp_magic(netmem) & PP_MAGIC_MASK) == PP_SIGNATURE;
 }
 
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 1a5edec485f1..2756b78754b0 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -699,7 +699,13 @@ s32 page_pool_inflight(const struct page_pool *pool, bool strict)
 void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
 {
 	netmem_set_pp(netmem, pool);
-	netmem_or_pp_magic(netmem, PP_SIGNATURE);
+
+	/* For page-backed, pp_magic is used to identify if it's pp.
+	 * For net_iov, it's ensured nmdesc->pp is non-NULL if it's pp
+	 * and nmdesc->pp is NULL if it's not.
+	 */
+	if (!netmem_is_net_iov(netmem))
+		netmem_or_pp_magic(netmem, PP_SIGNATURE);
 
 	/* Ensuring all pages have been split into one fragment initially:
 	 * page_pool_set_pp_info() is only called once for every page when it
@@ -714,7 +720,13 @@ 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);
+	/* For page-backed, pp_magic is used to identify if it's pp.
+	 * For net_iov, it's ensured nmdesc->pp is non-NULL if it's pp
+	 * and nmdesc->pp is NULL if it's not.
+	 */
+	if (!netmem_is_net_iov(netmem))
+		netmem_clear_pp_magic(netmem);
+
 	netmem_set_pp(netmem, NULL);
 }
 
-- 
2.17.1

[RFC mm v4 2/2] mm: introduce a new page type for page pool in page type

[Byungchul Park]

->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@redhat.com>
Co-developed-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Byungchul Park <byungchul@sk.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Zi Yan <ziy@nvidia.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) |
 			(page->flags.f & 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 +1376,12 @@ __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))
diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h
index 5561fd556bc5..664a9fe87c66 100644
--- a/net/core/netmem_priv.h
+++ b/net/core/netmem_priv.h
@@ -8,18 +8,6 @@ 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)
 {
 	/* net_iov may be part of a page pool.  For net_iov, ->pp in
@@ -30,7 +18,10 @@ static inline bool netmem_is_pp(netmem_ref netmem)
 	if (netmem_is_net_iov(netmem))
 		return !!netmem_to_nmdesc(netmem)->pp;
 
-	return (netmem_get_pp_magic(netmem) & PP_MAGIC_MASK) == PP_SIGNATURE;
+	/* For system memory, page type in struct page can be used to
+	 * determine if the pages belong to a page pool.
+	 */
+	return PageNetpp(__netmem_to_page(netmem));
 }
 
 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 2756b78754b0..c43a0f4479d4 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -700,12 +700,11 @@ void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
 {
 	netmem_set_pp(netmem, pool);
 
-	/* For page-backed, pp_magic is used to identify if it's pp.
-	 * For net_iov, it's ensured nmdesc->pp is non-NULL if it's pp
-	 * and nmdesc->pp is NULL if it's not.
+	/* For system memory, page type in struct page is used to
+	 * determine if the pages belong to a page pool.
 	 */
 	if (!netmem_is_net_iov(netmem))
-		netmem_or_pp_magic(netmem, PP_SIGNATURE);
+		__SetPageNetpp(__netmem_to_page(netmem));
 
 	/* Ensuring all pages have been split into one fragment initially:
 	 * page_pool_set_pp_info() is only called once for every page when it
@@ -720,12 +719,11 @@ void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem)
 
 void page_pool_clear_pp_info(netmem_ref netmem)
 {
-	/* For page-backed, pp_magic is used to identify if it's pp.
-	 * For net_iov, it's ensured nmdesc->pp is non-NULL if it's pp
-	 * and nmdesc->pp is NULL if it's not.
+	/* For system memory, page type in struct page is used to
+	 * determine if the pages belong to a page pool.
 	 */
 	if (!netmem_is_net_iov(netmem))
-		netmem_clear_pp_magic(netmem);
+		__ClearPageNetpp(__netmem_to_page(netmem));
 
 	netmem_set_pp(netmem, NULL);
 }
-- 
2.17.1

Re: [RFC mm v4 1/2] page_pool: check if nmdesc->pp is !NULL to confirm its usage as pp for net_iov

[Mina Almasry]

On Thu, Oct 23, 2025 at 12:44 AM Byungchul Park <byungchul@sk.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.g. PGTY_netpp should be used for that purpose.
>
> As a preparation, the check for net_iov, that is not page-backed, should
> avoid using ->pp_magic since net_iov doens't have to do with page type.
> Instead, nmdesc->pp can be used if a net_iov or its nmdesc belongs to a
> page pool, by making sure nmdesc->pp is NULL otherwise.
>
> For page-backed netmem, just leave unchanged as is, while for net_iov,
> make sure nmdesc->pp is initialized to NULL and use nmdesc->pp for the
> check.
>
> Signed-off-by: Byungchul Park <byungchul@sk.com>
> ---
>  net/core/devmem.c      |  1 +
>  net/core/netmem_priv.h |  8 ++++++++
>  net/core/page_pool.c   | 16 ++++++++++++++--
>  3 files changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/devmem.c b/net/core/devmem.c
> index d9de31a6cc7f..f81b700f1fd1 100644
> --- a/net/core/devmem.c
> +++ b/net/core/devmem.c
> @@ -291,6 +291,7 @@ net_devmem_bind_dmabuf(struct net_device *dev,
>                         niov = &owner->area.niovs[i];
>                         niov->type = NET_IOV_DMABUF;
>                         niov->owner = &owner->area;
> +                       niov->desc.pp = NULL;

Don't you also need to = NULL the niov allocations in io_uring zcrx,
or is that already done? Maybe mention in commit message.

Other than that, looks correct,

Reviewed-by: Mina Almasry <almasrymina@google.com>

Re: [RFC mm v4 2/2] mm: introduce a new page type for page pool in page type

[Mina Almasry]

On Thu, Oct 23, 2025 at 12:45 AM Byungchul Park <byungchul@sk.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@redhat.com>
> Co-developed-by: Pavel Begunkov <asml.silence@gmail.com>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> Signed-off-by: Byungchul Park <byungchul@sk.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Acked-by: Zi Yan <ziy@nvidia.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?

Re: [RFC mm v4 2/2] mm: introduce a new page type for page pool in page type

[Zi Yan]

On 27 Oct 2025, at 21:28, Mina Almasry wrote:

> On Thu, Oct 23, 2025 at 12:45 AM Byungchul Park <byungchul@sk.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@redhat.com>
>> Co-developed-by: Pavel Begunkov <asml.silence@gmail.com>
>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>> Signed-off-by: Byungchul Park <byungchul@sk.com>
>> Acked-by: David Hildenbrand <david@redhat.com>
>> Acked-by: Zi Yan <ziy@nvidia.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

Re: [RFC mm v4 1/2] page_pool: check if nmdesc->pp is !NULL to confirm its usage as pp for net_iov

[Byungchul Park]

On Mon, Oct 27, 2025 at 06:25:38PM -0700, Mina Almasry wrote:
> On Thu, Oct 23, 2025 at 12:44 AM Byungchul Park <byungchul@sk.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.g. PGTY_netpp should be used for that purpose.
> >
> > As a preparation, the check for net_iov, that is not page-backed, should
> > avoid using ->pp_magic since net_iov doens't have to do with page type.
> > Instead, nmdesc->pp can be used if a net_iov or its nmdesc belongs to a
> > page pool, by making sure nmdesc->pp is NULL otherwise.
> >
> > For page-backed netmem, just leave unchanged as is, while for net_iov,
> > make sure nmdesc->pp is initialized to NULL and use nmdesc->pp for the
> > check.
> >
> > Signed-off-by: Byungchul Park <byungchul@sk.com>
> > ---
> >  net/core/devmem.c      |  1 +
> >  net/core/netmem_priv.h |  8 ++++++++
> >  net/core/page_pool.c   | 16 ++++++++++++++--
> >  3 files changed, 23 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/core/devmem.c b/net/core/devmem.c
> > index d9de31a6cc7f..f81b700f1fd1 100644
> > --- a/net/core/devmem.c
> > +++ b/net/core/devmem.c
> > @@ -291,6 +291,7 @@ net_devmem_bind_dmabuf(struct net_device *dev,
> >                         niov = &owner->area.niovs[i];
> >                         niov->type = NET_IOV_DMABUF;
> >                         niov->owner = &owner->area;
> > +                       niov->desc.pp = NULL;
> 
> Don't you also need to = NULL the niov allocations in io_uring zcrx,
> or is that already done? Maybe mention in commit message.

Yes, that's been already done by kvmalloc_array(__GFP_ZERO).  I want to
leave a comment explaining that on io_uring side like:

diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index e5ff49f3425e..f771bb3e756d 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -444,6 +444,10 @@ static int io_zcrx_create_area(struct io_zcrx_ifq *ifq,
 		area->freelist[i] = i;
 		atomic_set(&area->user_refs[i], 0);
 		niov->type = NET_IOV_IOURING;
+
+		/* niov->pp is already initialized to NULL by
+		 * kvmalloc_array(__GFP_ZERO).
+		 */
 	}
 
 	area->free_count = nr_iovs;

However, I dropped it as Pavel requested:

  https://lore.kernel.org/lkml/8d833a3f-ae18-4ea6-9092-ddaa48290a63@gmail.com/

I will mention it in commit message then.

> Other than that, looks correct,
> 
> Reviewed-by: Mina Almasry <almasrymina@google.com>

Thanks.

	Byungchul

Re: [RFC mm v4 2/2] mm: introduce a new page type for page pool in page type

[Mina Almasry]

On Mon, Oct 27, 2025 at 6:45 PM Zi Yan <ziy@nvidia.com> wrote:
>
> On 27 Oct 2025, at 21:28, Mina Almasry wrote:
>
> > On Thu, Oct 23, 2025 at 12:45 AM Byungchul Park <byungchul@sk.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@redhat.com>
> >> Co-developed-by: Pavel Begunkov <asml.silence@gmail.com>
> >> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> >> Signed-off-by: Byungchul Park <byungchul@sk.com>
> >> Acked-by: David Hildenbrand <david@redhat.com>
> >> Acked-by: Zi Yan <ziy@nvidia.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@google.com>

-- 
Thanks,
Mina

Re: [RFC mm v4 1/2] page_pool: check if nmdesc->pp is !NULL to confirm its usage as pp for net_iov

[Jakub Kicinski]

On Thu, 23 Oct 2025 16:44:09 +0900 Byungchul Park wrote:
> As a preparation, the check for net_iov, that is not page-backed, should
> avoid using ->pp_magic since net_iov doens't have to do with page type.

doesn't

> Instead, nmdesc->pp can be used if a net_iov or its nmdesc belongs to a
> page pool, by making sure nmdesc->pp is NULL otherwise.

Please explain in the commit message why the new branch in
netmem_is_pp() is necessary. We used to identify the pages based
on PP_SIGNATURE, now we identify them based on page_type.

Re: [RFC mm v4 1/2] page_pool: check if nmdesc->pp is !NULL to confirm its usage as pp for net_iov

[Byungchul Park]

On Tue, Oct 28, 2025 at 06:33:56PM -0700, Jakub Kicinski wrote:
> On Thu, 23 Oct 2025 16:44:09 +0900 Byungchul Park wrote:
> > As a preparation, the check for net_iov, that is not page-backed, should
> > avoid using ->pp_magic since net_iov doens't have to do with page type.
> 
> doesn't
> 
> > Instead, nmdesc->pp can be used if a net_iov or its nmdesc belongs to a
> > page pool, by making sure nmdesc->pp is NULL otherwise.
> 
> Please explain in the commit message why the new branch in
> netmem_is_pp() is necessary. We used to identify the pages based
> on PP_SIGNATURE, now we identify them based on page_type.

Yes, I will.  It'd be much better.  Thank you very much for the comment.

	Byungchul