netns: reorder fields in struct net

In a network bench, I noticed an unfortunate false sharing between
'loopback_dev' and 'count' fields in "struct net".

'count' is written each time a socket is created or destroyed, while
loopback_dev might be often read in routing code.

Move loopback_dev in a read mostly section of "struct net"

Note: struct netns_xfrm is cache line aligned on SMP.
(It contains a "struct dst_ops")
Move it at the end to avoid holes, and reduce sizeof(struct net) by 128
bytes on ia32.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 4 deletions

diff --git a/include/net/netns/xfrm.h b/include/net/netns/xfrm.h
index 74f119a2829a..748f91f87cd5 100644
--- a/include/net/netns/xfrm.h
+++ b/include/net/netns/xfrm.h
@@ -43,10 +43,6 @@ struct netns_xfrm {
         unsigned int            policy_count[XFRM_POLICY_MAX * 2];
         struct work_struct      policy_hash_work;
 
-        struct dst_ops          xfrm4_dst_ops;
-#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
-        struct dst_ops          xfrm6_dst_ops;
-#endif
 
         struct sock             *nlsk;
         struct sock             *nlsk_stash;
@@ -58,6 +54,11 @@ struct netns_xfrm {
 #ifdef CONFIG_SYSCTL
         struct ctl_table_header *sysctl_hdr;
 #endif
+
+        struct dst_ops          xfrm4_dst_ops;
+#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
+        struct dst_ops          xfrm6_dst_ops;
+#endif
 };
 
 #endif