net: add struct net_aligned_data

This structure will hold networking data that must
consume a full cache line to avoid accidental false sharing.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250630093540.3052835-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/aligned_data.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _NET_ALIGNED_DATA_H
+#define _NET_ALIGNED_DATA_H
+
+#include <linux/types.h>
+
+/* Structure holding cacheline aligned fields on SMP builds.
+ * Each field or group should have an ____cacheline_aligned_in_smp
+ * attribute to ensure no accidental false sharing can happen.
+ */
+struct net_aligned_data {
+};
+
+extern struct net_aligned_data net_aligned_data;
+
+#endif /* _NET_ALIGNED_DATA_H */

net/core/hotdata.c

@@ -2,6 +2,7 @@
 #include <linux/cache.h>
 #include <linux/jiffies.h>
 #include <linux/list.h>
+#include <net/aligned_data.h>
 #include <net/hotdata.h>
 #include <net/proto_memory.h>
 
@@ -22,3 +23,5 @@ struct net_hotdata net_hotdata __cacheline_aligned = {
 	.sysctl_mem_pcpu_rsv = SK_MEMORY_PCPU_RESERVE
 };
 EXPORT_SYMBOL(net_hotdata);
+
+struct net_aligned_data net_aligned_data;