[PATCH net-next] netlabel: Reorder fields in 'struct netlbl_domaddr6_map'

[PATCH net-next] netlabel: Reorder fields in 'struct netlbl_domaddr6_map'

[Christophe JAILLET]

Group some variables based on their sizes to reduce hole and avoid padding.
On x86_64, this shrinks the size of 'struct netlbl_domaddr6_map'
from 72 to 64 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 netlbl_dom_map {
	char *                     domain;               /*     0     8 */
	u16                        family;               /*     8     2 */

	/* XXX 6 bytes hole, try to pack */

	struct netlbl_dommap_def   def;                  /*    16    16 */
	u32                        valid;                /*    32     4 */

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

	struct list_head           list;                 /*    40    16 */
	struct callback_head       rcu __attribute__((__aligned__(8))); /*    56    16 */

	/* size: 72, cachelines: 2, members: 6 */
	/* sum members: 62, holes: 2, sum holes: 10 */
	/* forced alignments: 1 */
	/* last cacheline: 8 bytes */
} __attribute__((__aligned__(8)));


After:
=====
struct netlbl_dom_map {
	char *                     domain;               /*     0     8 */
	struct netlbl_dommap_def   def;                  /*     8    16 */
	u16                        family;               /*    24     2 */

	/* XXX 2 bytes hole, try to pack */

	u32                        valid;                /*    28     4 */
	struct list_head           list;                 /*    32    16 */
	struct callback_head       rcu __attribute__((__aligned__(8))); /*    48    16 */

	/* size: 64, cachelines: 1, members: 6 */
	/* sum members: 62, holes: 1, sum holes: 2 */
	/* forced alignments: 1 */
} __attribute__((__aligned__(8)));
---
 net/netlabel/netlabel_domainhash.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netlabel/netlabel_domainhash.h b/net/netlabel/netlabel_domainhash.h
index 9f80972ae39b..7eaa35fdd9bd 100644
--- a/net/netlabel/netlabel_domainhash.h
+++ b/net/netlabel/netlabel_domainhash.h
@@ -57,8 +57,8 @@ struct netlbl_domaddr6_map {
 
 struct netlbl_dom_map {
 	char *domain;
-	u16 family;
 	struct netlbl_dommap_def def;
+	u16 family;
 
 	u32 valid;
 	struct list_head list;
-- 
2.34.1

Re: [PATCH net-next] netlabel: Reorder fields in 'struct netlbl_domaddr6_map'

[Simon Horman]

On Sun, Jun 18, 2023 at 12:16:41PM +0200, Christophe JAILLET wrote:
> Group some variables based on their sizes to reduce hole and avoid padding.
> On x86_64, this shrinks the size of 'struct netlbl_domaddr6_map'
> from 72 to 64 bytes.
> 
> It saves a few bytes of memory and is more cache-line friendly.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>

Reviewed-by: Simon Horman <simon.horman@corigine.com>

Re: [PATCH net-next] netlabel: Reorder fields in 'struct netlbl_domaddr6_map'

[Jiri Pirko]

Sun, Jun 18, 2023 at 12:16:41PM CEST, christophe.jaillet@wanadoo.fr wrote:
>Group some variables based on their sizes to reduce hole and avoid padding.
>On x86_64, this shrinks the size of 'struct netlbl_domaddr6_map'
>from 72 to 64 bytes.
>
>It saves a few bytes of memory and is more cache-line friendly.
>
>Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>

Reviewed-by: Jiri Pirko <jiri@nvidia.com>

Re: [PATCH net-next] netlabel: Reorder fields in 'struct netlbl_domaddr6_map'

[Paul Moore]

On Sun, Jun 18, 2023 at 6:16 AM Christophe JAILLET
<christophe.jaillet@wanadoo.fr> wrote:
>
> Group some variables based on their sizes to reduce hole and avoid padding.
> On x86_64, this shrinks the size of 'struct netlbl_domaddr6_map'
> from 72 to 64 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 netlbl_dom_map {
>         char *                     domain;               /*     0     8 */
>         u16                        family;               /*     8     2 */
>
>         /* XXX 6 bytes hole, try to pack */
>
>         struct netlbl_dommap_def   def;                  /*    16    16 */
>         u32                        valid;                /*    32     4 */
>
>         /* XXX 4 bytes hole, try to pack */
>
>         struct list_head           list;                 /*    40    16 */
>         struct callback_head       rcu __attribute__((__aligned__(8))); /*    56    16 */
>
>         /* size: 72, cachelines: 2, members: 6 */
>         /* sum members: 62, holes: 2, sum holes: 10 */
>         /* forced alignments: 1 */
>         /* last cacheline: 8 bytes */
> } __attribute__((__aligned__(8)));
>
>
> After:
> =====
> struct netlbl_dom_map {
>         char *                     domain;               /*     0     8 */
>         struct netlbl_dommap_def   def;                  /*     8    16 */
>         u16                        family;               /*    24     2 */
>
>         /* XXX 2 bytes hole, try to pack */
>
>         u32                        valid;                /*    28     4 */
>         struct list_head           list;                 /*    32    16 */
>         struct callback_head       rcu __attribute__((__aligned__(8))); /*    48    16 */
>
>         /* size: 64, cachelines: 1, members: 6 */
>         /* sum members: 62, holes: 1, sum holes: 2 */
>         /* forced alignments: 1 */
> } __attribute__((__aligned__(8)));
> ---
>  net/netlabel/netlabel_domainhash.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Acked-by: Paul Moore <paul@paul-moore.com>

-- 
paul-moore.com

Re: [PATCH net-next] netlabel: Reorder fields in 'struct netlbl_domaddr6_map'

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Sun, 18 Jun 2023 12:16:41 +0200 you wrote:
> Group some variables based on their sizes to reduce hole and avoid padding.
> On x86_64, this shrinks the size of 'struct netlbl_domaddr6_map'
> from 72 to 64 bytes.
> 
> It saves a few bytes of memory and is more cache-line friendly.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> 
> [...]

Here is the summary with links:
  - [net-next] netlabel: Reorder fields in 'struct netlbl_domaddr6_map'
    https://git.kernel.org/netdev/net-next/c/f0d952646bcf

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html