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Message-Id: <20250529031047.7587-2-byungchul@sk.com>
Date: Thu, 29 May 2025 12:10:30 +0900
From: Byungchul Park <byungchul@...com>
To: willy@...radead.org,
netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
linux-mm@...ck.org,
kernel_team@...ynix.com,
kuba@...nel.org,
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Subject: [RFC v3 01/18] netmem: introduce struct netmem_desc mirroring struct page
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 and make it union'ed with the existing fields in struct
net_iov, allowing to organize the fields of struct net_iov. The final
look of struct net_iov should be like:
struct net_iov {
struct netmem_desc;
net_field1; /* e.g. struct net_iov_area *owner; */
net_field2;
...
};
Signed-off-by: Byungchul Park <byungchul@...com>
---
include/net/netmem.h | 101 +++++++++++++++++++++++++++++++++----------
1 file changed, 79 insertions(+), 22 deletions(-)
diff --git a/include/net/netmem.h b/include/net/netmem.h
index 386164fb9c18..d52f86082271 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -12,6 +12,47 @@
#include <linux/mm.h>
#include <net/net_debug.h>
+/* These fields in struct page are used by the page_pool and net stack:
+ *
+ * struct {
+ * unsigned long pp_magic;
+ * struct page_pool *pp;
+ * unsigned long _pp_mapping_pad;
+ * 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 netmem_desc.
+ */
+struct netmem_desc {
+ unsigned long _flags;
+ unsigned long pp_magic;
+ struct page_pool *pp;
+ unsigned long _pp_mapping_pad;
+ unsigned long dma_addr;
+ atomic_long_t pp_ref_count;
+};
+
+#define NETMEM_DESC_ASSERT_OFFSET(pg, desc) \
+ static_assert(offsetof(struct page, pg) == \
+ offsetof(struct netmem_desc, desc))
+NETMEM_DESC_ASSERT_OFFSET(flags, _flags);
+NETMEM_DESC_ASSERT_OFFSET(pp_magic, pp_magic);
+NETMEM_DESC_ASSERT_OFFSET(pp, pp);
+NETMEM_DESC_ASSERT_OFFSET(_pp_mapping_pad, _pp_mapping_pad);
+NETMEM_DESC_ASSERT_OFFSET(dma_addr, dma_addr);
+NETMEM_DESC_ASSERT_OFFSET(pp_ref_count, pp_ref_count);
+#undef NETMEM_DESC_ASSERT_OFFSET
+
+/*
+ * Since struct netmem_desc uses the space in struct page, the size
+ * should be checked, until struct netmem_desc has its own instance from
+ * slab, to avoid conflicting with other members within struct page.
+ */
+static_assert(sizeof(struct netmem_desc) <= offsetof(struct page, _refcount));
+
/* net_iov */
DECLARE_STATIC_KEY_FALSE(page_pool_mem_providers);
@@ -31,12 +72,33 @@ 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;
+ union {
+ struct netmem_desc desc;
+
+ /* XXX: The following part should be removed once all
+ * the references to them are converted so as to be
+ * accessed via netmem_desc e.g. niov->desc.pp instead
+ * of niov->pp.
+ *
+ * Plus, once struct netmem_desc has it own instance
+ * from slab, network's fields of the following can be
+ * moved out of struct netmem_desc like:
+ *
+ * struct net_iov {
+ * struct netmem_desc desc;
+ * struct net_iov_area *owner;
+ * ...
+ * };
+ */
+ struct {
+ 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;
+ };
+ };
};
struct net_iov_area {
@@ -48,27 +110,22 @@ struct net_iov_area {
unsigned long base_virtual;
};
-/* These fields in struct page are used by the page_pool and net stack:
+/* net_iov is union'ed with struct netmem_desc mirroring struct page, so
+ * the page_pool can access these fields without worrying whether the
+ * underlying fields are accessed via netmem_desc or directly via
+ * net_iov, until all the references to them are converted so as to be
+ * accessed via netmem_desc e.g. niov->desc.pp instead of niov->pp.
*
- * struct {
- * unsigned long pp_magic;
- * struct page_pool *pp;
- * unsigned long _pp_mapping_pad;
- * 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.
+ * The non-net stack fields of struct page are private to the mm stack
+ * and must never be mirrored to net_iov.
*/
-#define NET_IOV_ASSERT_OFFSET(pg, iov) \
- static_assert(offsetof(struct page, pg) == \
+#define NET_IOV_ASSERT_OFFSET(desc, iov) \
+ static_assert(offsetof(struct netmem_desc, desc) == \
offsetof(struct net_iov, iov))
+NET_IOV_ASSERT_OFFSET(_flags, type);
NET_IOV_ASSERT_OFFSET(pp_magic, pp_magic);
NET_IOV_ASSERT_OFFSET(pp, pp);
+NET_IOV_ASSERT_OFFSET(_pp_mapping_pad, owner);
NET_IOV_ASSERT_OFFSET(dma_addr, dma_addr);
NET_IOV_ASSERT_OFFSET(pp_ref_count, pp_ref_count);
#undef NET_IOV_ASSERT_OFFSET
--
2.17.1
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