net: move sysctl_skb_defer_max to net_hotdata

sysctl_skb_defer_max is used in TCP fast path,
move it to net_hodata.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240429134025.1233626-3-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/hotdata.h

@@ -39,6 +39,7 @@ struct net_hotdata {
 	int			dev_tx_weight;
 	int			dev_rx_weight;
 	int			sysctl_max_skb_frags;
+	int			sysctl_skb_defer_max;
 };
 
 #define inet_ehash_secret	net_hotdata.tcp_protocol.secret

net/core/dev.c

@@ -4450,7 +4450,6 @@ EXPORT_SYMBOL(__dev_direct_xmit);
  *************************************************************************/
 static DEFINE_PER_CPU(struct task_struct *, backlog_napi);
 
-unsigned int sysctl_skb_defer_max __read_mostly = 64;
 int weight_p __read_mostly = 64;           /* old backlog weight */
 int dev_weight_rx_bias __read_mostly = 1;  /* bias for backlog weight */
 int dev_weight_tx_bias __read_mostly = 1;  /* bias for output_queue quota */

net/core/dev.h

@@ -36,7 +36,6 @@ int dev_addr_init(struct net_device *dev);
 void dev_addr_check(struct net_device *dev);
 
 /* sysctls not referred to from outside net/core/ */
-extern unsigned int	sysctl_skb_defer_max;
 extern int		netdev_unregister_timeout_secs;
 extern int		weight_p;
 extern int		dev_weight_rx_bias;

net/core/hotdata.c

@@ -19,5 +19,6 @@ struct net_hotdata net_hotdata __cacheline_aligned = {
 	.dev_tx_weight = 64,
 	.dev_rx_weight = 64,
 	.sysctl_max_skb_frags = MAX_SKB_FRAGS,
+	.sysctl_skb_defer_max = 64,
 };
 EXPORT_SYMBOL(net_hotdata);

net/core/skbuff.c

@@ -6985,7 +6985,7 @@ nodefer:	kfree_skb_napi_cache(skb);
 	DEBUG_NET_WARN_ON_ONCE(skb->destructor);
 
 	sd = &per_cpu(softnet_data, cpu);
-	defer_max = READ_ONCE(sysctl_skb_defer_max);
+	defer_max = READ_ONCE(net_hotdata.sysctl_skb_defer_max);
 	if (READ_ONCE(sd->defer_count) >= defer_max)
 		goto nodefer;
 

net/core/sysctl_net_core.c

@@ -654,7 +654,7 @@ static struct ctl_table net_core_table[] = {
 	},
 	{
 		.procname	= "skb_defer_max",
-		.data		= &sysctl_skb_defer_max,
+		.data		= &net_hotdata.sysctl_skb_defer_max,
 		.maxlen		= sizeof(unsigned int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,