netns: introduce the net_hash_mix "salt" for hashes

There are many possible ways to add this "salt", thus I made this
patch to be the last in the series to change it if required.

Currently I propose to use the struct net pointer itself as this 
salt, but since this pointer is most often cache-line aligned, shift 
this right to eliminate the bits, that are most often zeroed.

After this, simply add this mix to prepared hashfn-s.

For CONFIG_NET_NS=n case this salt is 0 and no changes in hashfn
appear.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/udp.h b/include/linux/udp.h
index 3deccac2e815..0cf5c4c0ec81 100644
--- a/include/linux/udp.h
+++ b/include/linux/udp.h
@@ -38,6 +38,7 @@ struct udphdr {
 #ifdef __KERNEL__
 #include <net/inet_sock.h>
 #include <linux/skbuff.h>
+#include <net/netns/hash.h>
 
 static inline struct udphdr *udp_hdr(const struct sk_buff *skb)
 {
@@ -48,7 +49,7 @@ static inline struct udphdr *udp_hdr(const struct sk_buff *skb)
 
 static inline int udp_hashfn(struct net *net, const unsigned num)
 {
-        return num & (UDP_HTABLE_SIZE - 1);
+        return (num + net_hash_mix(net)) & (UDP_HTABLE_SIZE - 1);
 }
 
 struct udp_sock {