Re: [PATCH linux-next v3] mm, page_pool: introduce a new page type for page pool in page type

[Pavel Begunkov <asml.silence@gmail.com>]

On 8/13/25 07:09, Byungchul Park wrote:
> On Tue, Jul 29, 2025 at 08:02:10PM +0900, Byungchul Park wrote:
...>> 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.
> 
> Hi, Andrew and Jakub
> 
> I will spin the next one with some modified, once the following patch,
> [1], gets merged.
> 
>     [1] https://lore.kernel.org/all/a8643abedd208138d3d550db71631d5a2e4168d1.1754929026.git.asml.silence@gmail.com/
> 
> This is about both mm and network.  I have no idea which tree should I
> aim at between mm tree and network tree?  I prefer the network tree tho.
> 
> However, it's totally fine regardless of what it would be.  Suggestion?

It should go to net, there will be enough of conflicts otherwise.
mm maintainers, do you like it as a shared branch or can it just
go through the net tree?


It'd also be better to split mm and net changes into a separate
patches. A patch I had before, it might need a rebase though.

From: Pavel Begunkov <asml.silence@gmail.com>
Date: Thu, 17 Jul 2025 11:46:21 +0100
Subject: [PATCH] mm: introduce a page type for page pool

Page pool currently uses ->pp_magic aliased with lru.next to check
whether a page belongs to it. Add a new page type, a later patch will
convert page pool to use it.

Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
  include/linux/mm.h         | 20 --------------------
  include/linux/page-flags.h |  6 ++++++
  mm/page_alloc.c            |  7 +++----
  3 files changed, 9 insertions(+), 24 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0d4ee569aa6b..21db02e92b33 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4205,26 +4205,6 @@ 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..0afdf2ee3fbd 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_net_pp		= 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 pages allocated by page_pool. See (see net/core/page_pool.c)
+ */
+PAGE_TYPE_OPS(Net_pp, net_pp, net_pp)
+
  /**
   * PageHuge - Determine if the page belongs to hugetlbfs
   * @page: The page to test.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d1d037f97c5f..67dfd6d8a124 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(PageNet_pp(page));
  		/* Reset the page_type (which overlays _mapcount) */
  		page->page_type = UINT_MAX;
+	}
  
  	if (is_check_pages_enabled()) {
  		if (free_page_is_bad(page))

-- 
Pavel Begunkov