[PATCH net-next v2] tcp: remove unused hash_size from struct tcp_out_options

[PATCH net-next v2] tcp: remove unused hash_size from struct tcp_out_options

[Keita Morisaki]

hash_size is declared but never read. The MD5 path always uses a
fixed size of 16, and the TCP-AO path uses tcp_ao_maclen().

This closes a 7-byte hole and reduces the struct size from 96 to
88 bytes.

Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Keita Morisaki <kmta1236@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
---
Changes in v2:
  - Added struct size improvement details to commit message (Jakub)
  - Added Reviewed-by tag

 net/ipv4/tcp_output.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f0ebcc7e2..4377b3673 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -441,7 +441,6 @@ struct tcp_out_options {
 	u8 ws;			/* window scale, 0 to disable */
 	u8 num_accecn_fields:7,	/* number of AccECN fields needed */
 	   use_synack_ecn_bytes:1; /* Use synack_ecn_bytes or not */
-	u8 hash_size;		/* bytes in hash_location */
 	__u8 *hash_location;	/* temporary pointer, overloaded */
 	__u32 tsval, tsecr;	/* need to include OPTION_TS */
 	struct tcp_fastopen_cookie *fastopen_cookie;	/* Fast open cookie */

base-commit: f4ac0cc88e9949d41bbdd101caa3117afe983ec9
-- 
2.53.0

Re: [PATCH net-next v2] tcp: remove unused hash_size from struct tcp_out_options

[Eric Dumazet]

On Sat, Mar 7, 2026 at 6:16 AM Keita Morisaki <kmta1236@gmail.com> wrote:
>
> hash_size is declared but never read. The MD5 path always uses a
> fixed size of 16, and the TCP-AO path uses tcp_ao_maclen().
>
> This closes a 7-byte hole and reduces the struct size from 96 to
> 88 bytes.
>
> Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
> Signed-off-by: Keita Morisaki <kmta1236@gmail.com>
> Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
> ---

Reviewed-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH net-next v2] tcp: remove unused hash_size from struct tcp_out_options

[patchwork-bot+netdevbpf]

Hello:

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

On Sat,  7 Mar 2026 14:16:19 +0900 you wrote:
> hash_size is declared but never read. The MD5 path always uses a
> fixed size of 16, and the TCP-AO path uses tcp_ao_maclen().
> 
> This closes a 7-byte hole and reduces the struct size from 96 to
> 88 bytes.
> 
> Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
> Signed-off-by: Keita Morisaki <kmta1236@gmail.com>
> Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
> 
> [...]

Here is the summary with links:
  - [net-next,v2] tcp: remove unused hash_size from struct tcp_out_options
    https://git.kernel.org/netdev/net-next/c/8ca8eb057673

You are awesome, thank you!
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