udp: dynamically size hash tables at boot time

UDP_HTABLE_SIZE was initialy defined to 128, which is a bit small for
several setups.

4000 active UDP sockets -> 32 sockets per chain in average. An
incoming frame has to lookup all sockets to find best match, so long
chains hurt latency.

Instead of a fixed size hash table that cant be perfect for every
needs, let UDP stack choose its table size at boot time like tcp/ip
route, using alloc_large_system_hash() helper

Add an optional boot parameter, uhash_entries=x so that an admin can
force a size between 256 and 65536 if needed, like thash_entries and
rhash_entries.

dmesg logs two new lines :
[    0.647039] UDP hash table entries: 512 (order: 0, 4096 bytes)
[    0.647099] UDP Lite hash table entries: 512 (order: 0, 4096 bytes)

Maximal size on 64bit arches would be 65536 slots, ie 1 MBytes for non
debugging spinlocks.

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

1 files changed, 3 insertions, 3 deletions

diff --git a/include/linux/udp.h b/include/linux/udp.h
index 0cf5c4c0ec81..832361e3e596 100644
--- a/include/linux/udp.h
+++ b/include/linux/udp.h
@@ -45,11 +45,11 @@ static inline struct udphdr *udp_hdr(const struct sk_buff *skb)
         return (struct udphdr *)skb_transport_header(skb);
 }
 
-#define UDP_HTABLE_SIZE         128
+#define UDP_HTABLE_SIZE_MIN             (CONFIG_BASE_SMALL ? 128 : 256)
 
-static inline int udp_hashfn(struct net *net, const unsigned num)
+static inline int udp_hashfn(struct net *net, unsigned num, unsigned mask)
 {
-        return (num + net_hash_mix(net)) & (UDP_HTABLE_SIZE - 1);
+        return (num + net_hash_mix(net)) & mask;
 }
 
 struct udp_sock {