netdev - [PATCH net-next] xfrm: reduce struct sec

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Message-ID: <83846bd2e3fa08899bd0162e41bfadfec95e82ef.1770398071.git.pabeni@redhat.com>
Date: Fri,  6 Feb 2026 18:14:36 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: netdev@...r.kernel.org
Cc: Steffen Klassert <steffen.klassert@...unet.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Simon Horman <horms@...nel.org>,
	Florian Westphal <fw@...len.de>
Subject: [PATCH net-next] xfrm: reduce struct sec_path size

The mentioned struct has an hole and uses unnecessary wide type to
store MAC length and indexes of very small arrays.

It's also embedded into the skb_extensions, and the latter, due
to recent CAN changes, may exceeds the 192 bytes mark (3 cachelines
on x86_64 arch) on some reasonable configurations.

Reordering and the sec_path fields, shrinking xfrm_offload.orig_mac_len
to 16 bits and xfrm_offload.{len,olen,verified_cnt} to u8, we can save
16 bytes and keep skb_extensions size under control.

Before:

struct sec_path {
	int                        len;
	int                        olen;
	int                        verified_cnt;

	/* XXX 4 bytes hole, try to pack */$
	struct xfrm_state *        xvec[6];
	struct xfrm_offload ovec[1];

	/* size: 88, cachelines: 2, members: 5 */
	/* sum members: 84, holes: 1, sum holes: 4 */
	/* last cacheline: 24 bytes */
};

After:

struct sec_path {
	struct xfrm_state *        xvec[6];
	struct xfrm_offload        ovec[1];
	/* typedef u8 -> __u8 */ unsigned char              len;
	/* typedef u8 -> __u8 */ unsigned char              olen;
	/* typedef u8 -> __u8 */ unsigned char              verified_cnt;

	/* size: 72, cachelines: 2, members: 5 */
	/* padding: 1 */
	/* last cacheline: 8 bytes */
};

Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
RFC -> v1:
  - shrink lens fields - thanks Florian
- RFC: https://lore.kernel.org/netdev/a2552992ca2fa29754340eaa05b1a185fca7a381.1770309837.git.pabeni@redhat.com/
---
 include/net/xfrm.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 0a14daaa5dd4..10d3edde6b2f 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1156,19 +1156,19 @@ struct xfrm_offload {
 #define CRYPTO_INVALID_PROTOCOL			128
 
 	/* Used to keep whole l2 header for transport mode GRO */
-	__u32			orig_mac_len;
+	__u16			orig_mac_len;
 
 	__u8			proto;
 	__u8			inner_ipproto;
 };
 
 struct sec_path {
-	int			len;
-	int			olen;
-	int			verified_cnt;
-
 	struct xfrm_state	*xvec[XFRM_MAX_DEPTH];
 	struct xfrm_offload	ovec[XFRM_MAX_OFFLOAD_DEPTH];
+
+	u8			len;
+	u8			olen;
+	u8			verified_cnt;
 };
 
 struct sec_path *secpath_set(struct sk_buff *skb);
-- 
2.52.0