netdev - [PATCH net-next] tcp: shrink inet_connection_sock icsk_mtup enabled and probe

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Date:   Fri, 29 Jan 2021 13:54:38 -0500
From:   Neal Cardwell <ncardwell.kernel@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Neal Cardwell <ncardwell@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next] tcp: shrink inet_connection_sock icsk_mtup enabled and probe_size

From: Neal Cardwell <ncardwell@...gle.com>

This commit shrinks inet_connection_sock by 4 bytes, by shrinking
icsk_mtup.enabled from 32 bits to 1 bit, and shrinking
icsk_mtup.probe_size from s32 to an unsuigned 31 bit field.

This is to save space to compensate for the recent introduction of a
new u32 in inet_connection_sock, icsk_probes_tstamp, in the recent bug
fix commit 9d9b1ee0b2d1 ("tcp: fix TCP_USER_TIMEOUT with zero window").

This should not change functionality, since icsk_mtup.enabled is only
ever set to 0 or 1, and icsk_mtup.probe_size can only be either 0
or a positive MTU value returned by tcp_mss_to_mtu()

Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/inet_connection_sock.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index c11f80f328f1..10a625760de9 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -120,14 +120,14 @@ struct inet_connection_sock {
 		__u16		  rcv_mss;	 /* MSS used for delayed ACK decisions	   */
 	} icsk_ack;
 	struct {
-		int		  enabled;
-
 		/* Range of MTUs to search */
 		int		  search_high;
 		int		  search_low;
 
 		/* Information on the current probe. */
-		int		  probe_size;
+		u32		  probe_size:31,
+		/* Is the MTUP feature enabled for this connection? */
+				  enabled:1;
 
 		u32		  probe_timestamp;
 	} icsk_mtup;
-- 
2.30.0.365.g02bc693789-goog