net: move net_cookie into net_aligned_data

Using per-cpu data for net->net_cookie generation is overkill,
because even busy hosts do not create hundreds of netns per second.

Make sure to put net_cookie in a private cache line to avoid
potential false sharing.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250630093540.3052835-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/aligned_data.h b/include/net/aligned_data.h
index cf3329d7c2272ec4424e89352626800cbc282663..5c7badf71f043a2bbc871b0063c9a2d2a4ffbfcb 100644 (file)
--- a/include/net/aligned_data.h
+++ b/include/net/aligned_data.h
@@ -2,6 +2,7 @@
 #ifndef _NET_ALIGNED_DATA_H
 #define _NET_ALIGNED_DATA_H
 
+#include <linux/atomic.h>
 #include <linux/types.h>
 
 /* Structure holding cacheline aligned fields on SMP builds.
@@ -9,6 +10,7 @@
  * attribute to ensure no accidental false sharing can happen.
  */
 struct net_aligned_data {
+       atomic64_t      net_cookie ____cacheline_aligned_in_smp;
 };
 
 extern struct net_aligned_data net_aligned_data;

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 419604d9cf32e2e2a9af59dfef1fbcc7fab81e20..f58ef920a3a18c6c98328885d6b91243632fc0b6 100644 (file)
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -19,9 +19,9 @@
 #include <linux/net_namespace.h>
 #include <linux/sched/task.h>
 #include <linux/uidgid.h>
-#include <linux/cookie.h>
 #include <linux/proc_fs.h>
 
+#include <net/aligned_data.h>
 #include <net/sock.h>
 #include <net/netlink.h>
 #include <net/net_namespace.h>
@@ -64,8 +64,6 @@ DECLARE_RWSEM(pernet_ops_rwsem);
 
 static unsigned int max_gen_ptrs = INITIAL_NET_GEN_PTRS;
 
-DEFINE_COOKIE(net_cookie);
-
 static struct net_generic *net_alloc_generic(void)
 {
        unsigned int gen_ptrs = READ_ONCE(max_gen_ptrs);
@@ -434,9 +432,7 @@ static __net_init int setup_net(struct net *net)
        LIST_HEAD(net_exit_list);
        int error = 0;
 
-       preempt_disable();
-       net->net_cookie = gen_cookie_next(&net_cookie);
-       preempt_enable();
+       net->net_cookie = atomic64_inc_return(&net_aligned_data.net_cookie);
 
        list_for_each_entry(ops, &pernet_list, list) {
                error = ops_init(ops, net);