Re: [PATCH] mm, page_pool: introduce a new page type for page pool in page type

On Mon, Jul 21, 2025 at 10:05:25AM +0200, David Hildenbrand wrote:

On 21.07.25 07:49, Byungchul Park wrote:

quoted

Hi,

I focused on converting the existing APIs accessing ->pp_magic field to
page type APIs.  However, yes.  Additional works would better be
considered on top like:

    1. Adjust how to store and retrieve dma index.  Maybe network guys
       can work better on top.

    2. Move the sanity check for page pool in mm/page_alloc.c to on free.

    Byungchul

---8<---
 From 7d207a1b3e9f4ff2a72f5b54b09e3ed0c4aaaca3 Mon Sep 17 00:00:00 2001
From: Byungchul Park <byungchul@sk.com>
Date: Mon, 21 Jul 2025 14:05:20 +0900
Subject: [PATCH] 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, page type e.i. PGTY_netpp can be used
for that purpose.

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() since they are totally replaced.

This work was inspired by the following link by Pavel:

[1] https://lore.kernel.org/all/582f41c0-2742-4400-9c81-0d46bf4e8314@gmail.com/ (local)

I'm, sure you saw my comment (including my earlier suggestion for using
a page type), in particular around ...

Honestly, I was too confused to understand exactly what you meant.
Maybe my bad but I was and I'm still so.  Lemme add a question below.

quoted

---
  .../net/ethernet/mellanox/mlx5/core/en/xdp.c  |  2 +-
  include/linux/mm.h                            | 28 ++-----------------
  include/linux/page-flags.h                    |  6 ++++
  include/net/netmem.h                          |  2 +-
  mm/page_alloc.c                               |  4 +--
  net/core/netmem_priv.h                        | 16 ++---------
  net/core/page_pool.c                          | 10 +++++--
  7 files changed, 24 insertions(+), 44 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 ae50c1641bed..736061749535 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -4135,10 +4135,9 @@ 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.
   *

@@ -4168,25 +4167,4 @@ 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
-
  #endif /* _LINUX_MM_H */

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 4fe5ee67535b..906ba7c9e372 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h

@@ -957,6 +957,7 @@ enum pagetype {
      PGTY_zsmalloc           = 0xf6,
      PGTY_unaccepted         = 0xf7,
      PGTY_large_kmalloc      = 0xf8,
+     PGTY_netpp              = 0xf9,

      PGTY_mapcount_underflow = 0xff
  };

@@ -1101,6 +1102,11 @@ 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 f7dacc9e75fd..3667334e16e7 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h

@@ -298,7 +298,7 @@ static inline struct net_iov *__netmem_clear_lsb(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 2ef3c07266b3..71c7666e48a9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c

@@ -898,7 +898,7 @@ static inline bool page_expected_state(struct page *page,
  #ifdef CONFIG_MEMCG
                      page->memcg_data |
  #endif
-                     page_pool_page_is_pp(page) |
+                     PageNetpp(page) |
                      (page->flags & check_flags)))
              return false;

@@ -925,7 +925,7 @@ 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)))
+     if (unlikely(PageNetpp(page)))
              bad_reason = "page_pool leak";
      return bad_reason;
  }

^ this

This will not work they way you want it once you rebase on top of
linux-next, where we have (from mm/mm-stable)

commit 2dfcd1608f3a96364f10de7fcfe28727c0292e5d

I just checked this.

So is it sufficient that I rebase on mm/mm-stable?  Or should I wait for
something else?  Or should I achieve this in other ways?

	Byungchul

Author: David Hildenbrand [off-list ref]
Date:   Fri Jul 4 12:24:58 2025 +0200

    mm/page_alloc: let page freeing clear any set page type


I commented what to do already.

--
Cheers,

David / dhildenb