netdev - [PATCH 01/18] netmem: introduce struct netmem_desc struct_group_tagged()'ed on struct net

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Message-Id: <20250523032609.16334-2-byungchul@sk.com>
Date: Fri, 23 May 2025 12:25:52 +0900
From: Byungchul Park <byungchul@...com>
To: willy@...radead.org,
	netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
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Subject: [PATCH 01/18] netmem: introduce struct netmem_desc struct_group_tagged()'ed on struct net_iov

To simplify struct page, the page pool members of struct page should be
moved to other, allowing these members to be removed from struct page.

Introduce a network memory descriptor to store the members, struct
netmem_desc, reusing struct net_iov that already mirrored struct page.

While at it, relocate _pp_mapping_pad to group struct net_iov's fields.

Signed-off-by: Byungchul Park <byungchul@...com>
---
 include/linux/mm_types.h |  2 +-
 include/net/netmem.h     | 43 +++++++++++++++++++++++++++++++++-------
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 56d07edd01f9..873e820e1521 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -120,13 +120,13 @@ struct page {
 			unsigned long private;
 		};
 		struct {	/* page_pool used by netstack */
+			unsigned long _pp_mapping_pad;
 			/**
 			 * @pp_magic: magic value to avoid recycling non
 			 * page_pool allocated pages.
 			 */
 			unsigned long pp_magic;
 			struct page_pool *pp;
-			unsigned long _pp_mapping_pad;
 			unsigned long dma_addr;
 			atomic_long_t pp_ref_count;
 		};
diff --git a/include/net/netmem.h b/include/net/netmem.h
index 386164fb9c18..08e9d76cdf14 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -31,12 +31,41 @@ enum net_iov_type {
 };
 
 struct net_iov {
-	enum net_iov_type type;
-	unsigned long pp_magic;
-	struct page_pool *pp;
-	struct net_iov_area *owner;
-	unsigned long dma_addr;
-	atomic_long_t pp_ref_count;
+	/*
+	 * XXX: Now that struct netmem_desc overlays on struct page,
+	 * struct_group_tagged() should cover all of them.  However,
+	 * a separate struct netmem_desc should be declared and embedded,
+	 * once struct netmem_desc is no longer overlayed but it has its
+	 * own instance from slab.  The final form should be:
+	 *
+	 *    struct netmem_desc {
+	 *	   unsigned long pp_magic;
+	 *	   struct page_pool *pp;
+	 *	   unsigned long dma_addr;
+	 *	   atomic_long_t pp_ref_count;
+	 *    };
+	 *
+	 *    struct net_iov {
+	 *	   enum net_iov_type type;
+	 *	   struct net_iov_area *owner;
+	 *	   struct netmem_desc;
+	 *    };
+	 */
+	struct_group_tagged(netmem_desc, desc,
+		/*
+		 * only for struct net_iov
+		 */
+		enum net_iov_type type;
+		struct net_iov_area *owner;
+
+		/*
+		 * actually for struct netmem_desc
+		 */
+		unsigned long pp_magic;
+		struct page_pool *pp;
+		unsigned long dma_addr;
+		atomic_long_t pp_ref_count;
+	);
 };
 
 struct net_iov_area {
@@ -51,9 +80,9 @@ struct net_iov_area {
 /* These fields in struct page are used by the page_pool and net stack:
  *
  *        struct {
+ *                unsigned long _pp_mapping_pad;
  *                unsigned long pp_magic;
  *                struct page_pool *pp;
- *                unsigned long _pp_mapping_pad;
  *                unsigned long dma_addr;
  *                atomic_long_t pp_ref_count;
  *        };
-- 
2.17.1