[PATCH 18/18] mm, netmem: remove the page pool members in struct page

[Byungchul Park <byungchul@xxxxxx>]

Now that all the users of the page pool members in struct page have been
gone, the members can be removed from struct page.

However, since struct netmem_desc might still use the space in struct
page, the size of struct netmem_desc should be checked, until struct
netmem_desc has its own instance from slab, to avoid conficting with
other members within struct page.

Remove the page pool members in struct page and add a static checker for
the size.

Signed-off-by: Byungchul Park <byungchul@xxxxxx>
---
 include/linux/mm_types.h | 11 -----------
 include/net/netmem.h     | 28 +++++-----------------------
 2 files changed, 5 insertions(+), 34 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 873e820e1521..5a7864eb9d76 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -119,17 +119,6 @@ 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 dma_addr;
-			atomic_long_t pp_ref_count;
-		};
 		struct {	/* Tail pages of compound page */
 			unsigned long compound_head;	/* Bit zero is set */
 		};
diff --git a/include/net/netmem.h b/include/net/netmem.h
index c63a7e20f5f3..257c22398d7a 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -77,30 +77,12 @@ struct net_iov_area {
 	unsigned long base_virtual;
 };
 
-/* 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 dma_addr;
- *                atomic_long_t pp_ref_count;
- *        };
- *
- * We mirror the page_pool fields here so the page_pool can access these fields
- * without worrying whether the underlying fields belong to a page or net_iov.
- *
- * The non-net stack fields of struct page are private to the mm stack and must
- * never be mirrored to net_iov.
+/* XXX: The page pool fields in struct page have been removed but they
+ * might still use the space in struct page.  Thus, the size of struct
+ * netmem_desc should be under control until struct netmem_desc has its
+ * own instance from slab.
  */
-#define NET_IOV_ASSERT_OFFSET(pg, iov)             \
-	static_assert(offsetof(struct page, pg) == \
-		      offsetof(struct net_iov, iov))
-NET_IOV_ASSERT_OFFSET(pp_magic, pp_magic);
-NET_IOV_ASSERT_OFFSET(pp, pp);
-NET_IOV_ASSERT_OFFSET(dma_addr, dma_addr);
-NET_IOV_ASSERT_OFFSET(pp_ref_count, pp_ref_count);
-#undef NET_IOV_ASSERT_OFFSET
+static_assert(sizeof(struct netmem_desc) <= offsetof(struct page, _refcount));
 
 static inline struct net_iov_area *net_iov_owner(const struct net_iov *niov)
 {
-- 
2.17.1