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, 2 insertions, 2 deletions

diff --git a/net/ipv4/udplite.c b/net/ipv4/udplite.c
index 95248d7f75e..470c504b955 100644
--- a/net/ipv4/udplite.c
+++ b/net/ipv4/udplite.c
@@ -12,7 +12,7 @@
  */
 #include "udp_impl.h"
 
-struct udp_table        udplite_table;
+struct udp_table        udplite_table __read_mostly;
 EXPORT_SYMBOL(udplite_table);
 
 static int udplite_rcv(struct sk_buff *skb)
@@ -110,7 +110,7 @@ static inline int udplite4_proc_init(void)
 
 void __init udplite4_register(void)
 {
-        udp_table_init(&udplite_table);
+        udp_table_init(&udplite_table, "UDP-Lite");
         if (proto_register(&udplite_prot, 1))
                 goto out_register_err;