net: move sysctl_max_skb_frags to net_hotdata

sysctl_max_skb_frags is used in TCP and MPTCP fast paths,
move it to net_hodata for better cache locality.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240429134025.1233626-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

7 files changed, 8 insertions, 9 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index adf75d69770c..36b133f04d30 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -353,8 +353,6 @@ struct sk_buff;
 
 #define MAX_SKB_FRAGS CONFIG_MAX_SKB_FRAGS
 
-extern int sysctl_max_skb_frags;
-
 /* Set skb_shinfo(skb)->gso_size to this in case you want skb_segment to
  * segment using its current segmentation instead.
  */
diff --git a/include/net/hotdata.h b/include/net/hotdata.h
index 003667a1efd6..a6cff6590426 100644
--- a/include/net/hotdata.h
+++ b/include/net/hotdata.h
@@ -38,6 +38,7 @@ struct net_hotdata {
 	int			max_backlog;
 	int			dev_tx_weight;
 	int			dev_rx_weight;
+	int			sysctl_max_skb_frags;
 };
 
 #define inet_ehash_secret	net_hotdata.tcp_protocol.secret
diff --git a/net/core/hotdata.c b/net/core/hotdata.c
index c8a7a451c18a..f17cbb4807b9 100644
--- a/net/core/hotdata.c
+++ b/net/core/hotdata.c
@@ -18,5 +18,6 @@ struct net_hotdata net_hotdata __cacheline_aligned = {
 	.max_backlog = 1000,
 	.dev_tx_weight = 64,
 	.dev_rx_weight = 64,
+	.sysctl_max_skb_frags = MAX_SKB_FRAGS,
 };
 EXPORT_SYMBOL(net_hotdata);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 0c8b82750000..65779b8f0b12 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -109,9 +109,6 @@ static struct kmem_cache *skbuff_ext_cache __ro_after_init;
 #define SKB_SMALL_HEAD_HEADROOM						\
 	SKB_WITH_OVERHEAD(SKB_SMALL_HEAD_CACHE_SIZE)
 
-int sysctl_max_skb_frags __read_mostly = MAX_SKB_FRAGS;
-EXPORT_SYMBOL(sysctl_max_skb_frags);
-
 /* kcm_write_msgs() relies on casting paged frags to bio_vec to use
  * iov_iter_bvec(). These static asserts ensure the cast is valid is long as the
  * netmem is a page.
@@ -7040,7 +7037,7 @@ static void skb_splice_csum_page(struct sk_buff *skb, struct page *page,
 ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter,
 			     ssize_t maxsize, gfp_t gfp)
 {
-	size_t frag_limit = READ_ONCE(sysctl_max_skb_frags);
+	size_t frag_limit = READ_ONCE(net_hotdata.sysctl_max_skb_frags);
 	struct page *pages[8], **ppages = pages;
 	ssize_t spliced = 0, ret = 0;
 	unsigned int i;
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 903ab4a51c17..e75375d54b9e 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -595,7 +595,7 @@ static struct ctl_table net_core_table[] = {
 	},
 	{
 		.procname	= "max_skb_frags",
-		.data		= &sysctl_max_skb_frags,
+		.data		= &net_hotdata.sysctl_max_skb_frags,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 4ec0f4feee00..388f6e115bf1 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -280,6 +280,7 @@
 #include <linux/uaccess.h>
 #include <asm/ioctls.h>
 #include <net/busy_poll.h>
+#include <net/hotdata.h>
 #include <net/rps.h>
 
 /* Track pending CMSGs. */
@@ -1188,7 +1189,7 @@ new_segment:
 
 			if (!skb_can_coalesce(skb, i, pfrag->page,
 					      pfrag->offset)) {
-				if (i >= READ_ONCE(sysctl_max_skb_frags)) {
+				if (i >= READ_ONCE(net_hotdata.sysctl_max_skb_frags)) {
 					tcp_mark_push(tp, skb);
 					goto new_segment;
 				}
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 4b13ca362efa..aff17597e6a7 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -20,6 +20,7 @@
 #include <net/transp_v6.h>
 #endif
 #include <net/mptcp.h>
+#include <net/hotdata.h>
 #include <net/xfrm.h>
 #include <asm/ioctls.h>
 #include "protocol.h"
@@ -1272,7 +1273,7 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
 
 		i = skb_shinfo(skb)->nr_frags;
 		can_coalesce = skb_can_coalesce(skb, i, dfrag->page, offset);
-		if (!can_coalesce && i >= READ_ONCE(sysctl_max_skb_frags)) {
+		if (!can_coalesce && i >= READ_ONCE(net_hotdata.sysctl_max_skb_frags)) {
 			tcp_mark_push(tcp_sk(ssk), skb);
 			goto alloc_skb;
 		}