netdev - [PATCH v2 net-next 2/4] net: move net_cookie into net_aligned

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Message-ID: <20250630093540.3052835-3-edumazet@google.com>
Date: Mon, 30 Jun 2025 09:35:38 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Willem de Bruijn <willemb@...gle.com>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH v2 net-next 2/4] 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@...gle.com>
Reviewed-by: Willem de Bruijn <willemb@...gle.com>
---
 include/net/aligned_data.h | 2 ++
 net/core/net_namespace.c   | 8 ++------
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/include/net/aligned_data.h b/include/net/aligned_data.h
index cf3329d7c2272ec4424e89352626800cbc282663..5c7badf71f043a2bbc871b0063c9a2d2a4ffbfcb 100644
--- 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 d0f607507ee8d0b6d31f11a49421b5f0a985bd3b..e68d208b200dd4be76fc08af73054b3d1dea834c 100644
--- 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);
-- 
2.50.0.727.gbf7dc18ff4-goog