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>
diff --git a/include/net/netns/hash.h b/include/net/netns/hash.h
new file mode 100644
index 0000000..548d78f
--- /dev/null
+++ b/include/net/netns/hash.h
@@ -0,0 +1,21 @@
+#ifndef __NET_NS_HASH_H__
+#define __NET_NS_HASH_H__
+
+#include <asm/cache.h>
+
+struct net;
+
+static inline unsigned net_hash_mix(struct net *net)
+{
+#ifdef CONFIG_NET_NS
+ /*
+ * shift this right to eliminate bits, that are
+ * always zeroed
+ */
+
+ return (unsigned)(((unsigned long)net) >> L1_CACHE_SHIFT);
+#else
+ return 0;
+#endif
+}
+#endif