tcp: shrink inet_connection_sock icsk_mtup enabled and probe_size

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@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20210129185438.1813237-1-ncardwell.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index c11f80f328f1d77212eb2ce5ab0b9e08dba3967b..10a625760de9128c57dbc047e6c766dd29069122 100644 (file)
--- 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;