netdev - [RFC PATCH] xfrm: reduce struct sec

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Message-ID: <a2552992ca2fa29754340eaa05b1a185fca7a381.1770309837.git.pabeni@redhat.com>
Date: Thu,  5 Feb 2026 17:44:14 +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>
Subject: [RFC PATCH] xfrm: reduce struct sec_path size

The mentioned struct has an hole and uses unnecessary wide type to
store a MAC length.

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 configuration.

Reordering and the sec_path fields and shrinking xfrm_offload.orig_mac_len
to 16 bits, we can save 8 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 {
	int                        len;
	int                        olen;
	struct xfrm_offload        ovec[1];
	int                        verified_cnt;
	struct xfrm_state *        xvec[6];

	/* size: 80, cachelines: 2, members: 5 */
	/* last cacheline: 16 bytes */
};

Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
only build tested, any feedback appreciated.
---
 include/net/xfrm.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 0a14daaa5dd4..41122cb83901 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1156,7 +1156,7 @@ 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;
@@ -1165,10 +1165,10 @@ struct xfrm_offload {
 struct sec_path {
 	int			len;
 	int			olen;
+	struct xfrm_offload	ovec[XFRM_MAX_OFFLOAD_DEPTH];
 	int			verified_cnt;
 
 	struct xfrm_state	*xvec[XFRM_MAX_DEPTH];
-	struct xfrm_offload	ovec[XFRM_MAX_OFFLOAD_DEPTH];
 };
 
 struct sec_path *secpath_set(struct sk_buff *skb);
-- 
2.52.0