[PATCH net-next] mptcp: Reorder fields in 'struct mptcp_pm_add_entry'

* [PATCH net-next] mptcp: Reorder fields in 'struct mptcp_pm_add_entry'
@ 2023-06-18  9:46 Christophe JAILLET
  2023-06-19 11:14 ` Matthieu Baerts
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Christophe JAILLET @ 2023-06-18  9:46 UTC (permalink / raw)
  To: Matthieu Baerts, Mat Martineau, David S. Miller, Eric Dumazet,
	Jakub Kicinski, Paolo Abeni
  Cc: linux-kernel, kernel-janitors, Christophe JAILLET, netdev, mptcp

Group some variables based on their sizes to reduce hole and avoid padding.
On x86_64, this shrinks the size of 'struct mptcp_pm_add_entry'
from 136 to 128 bytes.

It saves a few bytes of memory and is more cache-line friendly.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
Using pahole

Before:
======
struct mptcp_pm_add_entry {
	struct list_head           list;                 /*     0    16 */
	struct mptcp_addr_info     addr;                 /*    16    12 */

	/* XXX 4 bytes hole, try to pack */

	struct timer_list          add_timer;            /*    32    88 */
	/* --- cacheline 1 boundary (64 bytes) was 56 bytes ago --- */
	struct mptcp_sock *        sock;                 /*   120     8 */
	/* --- cacheline 2 boundary (128 bytes) --- */
	u8                         retrans_times;        /*   128     1 */

	/* size: 136, cachelines: 3, members: 5 */
	/* sum members: 125, holes: 1, sum holes: 4 */
	/* padding: 7 */
	/* last cacheline: 8 bytes */
};


After:
=====
struct mptcp_pm_add_entry {
	struct list_head           list;                 /*     0    16 */
	struct mptcp_addr_info     addr;                 /*    16    12 */
	u8                         retrans_times;        /*    28     1 */

	/* XXX 3 bytes hole, try to pack */

	struct timer_list          add_timer;            /*    32    88 */
	/* --- cacheline 1 boundary (64 bytes) was 56 bytes ago --- */
	struct mptcp_sock *        sock;                 /*   120     8 */

	/* size: 128, cachelines: 2, members: 5 */
	/* sum members: 125, holes: 1, sum holes: 3 */
};
---
 net/mptcp/pm_netlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index a12a87b780f6..a56718ffdd02 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -25,9 +25,9 @@ static int pm_nl_pernet_id;
 struct mptcp_pm_add_entry {
 	struct list_head	list;
 	struct mptcp_addr_info	addr;
+	u8			retrans_times;
 	struct timer_list	add_timer;
 	struct mptcp_sock	*sock;
-	u8			retrans_times;
 };
 
 struct pm_nl_pernet {
-- 
2.34.1


^ permalink raw reply related	[flat|nested] 4+ messages in thread