ipv6: Move ipv6_fl_list from ipv6_pinfo to inet_sock.

In {tcp6,udp6,raw6}_sock, struct ipv6_pinfo is always placed at
the beginning of a new cache line because

  1. __alignof__(struct tcp_sock) is 64 due to ____cacheline_aligned
     of __cacheline_group_begin(tcp_sock_write_tx)

  2. __alignof__(struct udp_sock) is 64 due to ____cacheline_aligned
     of struct numa_drop_counters

  3. in raw6_sock, struct numa_drop_counters is placed before
     struct ipv6_pinfo

.  struct ipv6_pinfo is 136 bytes, but the last cache line is
only used by ipv6_fl_list:

  $ pahole -C ipv6_pinfo vmlinux
  struct ipv6_pinfo {
  ...
  	/* --- cacheline 2 boundary (128 bytes) --- */
  	struct ipv6_fl_socklist *  ipv6_fl_list;         /*   128     8 */

  	/* size: 136, cachelines: 3, members: 23 */

Let's move ipv6_fl_list from struct ipv6_pinfo to struct inet_sock
to save a full cache line for {tcp6,udp6,raw6}_sock.

Now, struct ipv6_pinfo is 128 bytes, and {tcp6,udp6,raw6}_sock have
64 bytes less, while {tcp,udp,raw}_sock retain the same size.

Before:

  # grep -E "^(RAW|UDP[^L\-]|TCP)" /proc/slabinfo | awk '{print $1, "\t", $4}'
  RAWv6 	 1408
  UDPv6 	 1472
  TCPv6 	 2560
  RAW 		 1152
  UDP	 	 1280
  TCP 		 2368

After:

  # grep -E "^(RAW|UDP[^L\-]|TCP)" /proc/slabinfo | awk '{print $1, "\t", $4}'
  RAWv6 	 1344
  UDPv6 	 1408
  TCPv6 	 2496
  RAW 		 1152
  UDP	 	 1280
  TCP 		 2368

Also, ipv6_fl_list and inet_flags (SNDFLOW bit) are placed in the
same cache line.

  $ pahole -C inet_sock vmlinux
  ...
  	/* --- cacheline 11 boundary (704 bytes) was 56 bytes ago --- */
  	struct ipv6_pinfo *        pinet6;               /*   760     8 */
  	/* --- cacheline 12 boundary (768 bytes) --- */
  	struct ipv6_fl_socklist *  ipv6_fl_list;         /*   768     8 */
  	unsigned long              inet_flags;           /*   776     8 */

Doc churn is due to the insufficient Type column (only 1 space short).

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20251014224210.2964778-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
index 568ff8797c39..d725b2158758 100644
--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c
@@ -782,9 +782,10 @@ static struct sock *sctp_v6_create_accept_sk(struct sock *sk,
 					     struct sctp_association *asoc,
 					     bool kern)
 {
-	struct sock *newsk;
 	struct ipv6_pinfo *newnp, *np = inet6_sk(sk);
 	struct sctp6_sock *newsctp6sk;
+	struct inet_sock *newinet;
+	struct sock *newsk;
 
 	newsk = sk_alloc(sock_net(sk), PF_INET6, GFP_KERNEL, sk->sk_prot, kern);
 	if (!newsk)
@@ -796,7 +797,9 @@ static struct sock *sctp_v6_create_accept_sk(struct sock *sk,
 	sock_reset_flag(sk, SOCK_ZAPPED);
 
 	newsctp6sk = (struct sctp6_sock *)newsk;
-	inet_sk(newsk)->pinet6 = &newsctp6sk->inet6;
+	newinet = inet_sk(newsk);
+	newinet->pinet6 = &newsctp6sk->inet6;
+	newinet->ipv6_fl_list = NULL;
 
 	sctp_sk(newsk)->v4mapped = sctp_sk(sk)->v4mapped;
 
@@ -805,7 +808,6 @@ static struct sock *sctp_v6_create_accept_sk(struct sock *sk,
 	memcpy(newnp, np, sizeof(struct ipv6_pinfo));
 	newnp->ipv6_mc_list = NULL;
 	newnp->ipv6_ac_list = NULL;
-	newnp->ipv6_fl_list = NULL;
 
 	sctp_v6_copy_ip_options(sk, newsk);