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, 10 insertions, 3 deletions

diff --git a/include/net/udp.h b/include/net/udp.h
index f98abd2ce709..22aa2e7eb1d7 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -54,12 +54,19 @@ struct udp_hslot {
         struct hlist_nulls_head head;
         spinlock_t              lock;
 } __attribute__((aligned(2 * sizeof(long))));
+
 struct udp_table {
-        struct udp_hslot        hash[UDP_HTABLE_SIZE];
+        struct udp_hslot        *hash;
+        unsigned int mask;
+        unsigned int log;
 };
 extern struct udp_table udp_table;
-extern void udp_table_init(struct udp_table *);
-
+extern void udp_table_init(struct udp_table *, const char *);
+static inline struct udp_hslot *udp_hashslot(struct udp_table *table,
+                                             struct net *net, unsigned num)
+{
+        return &table->hash[udp_hashfn(net, num, table->mask)];
+}
 
 /* Note: this must match 'valbool' in sock_setsockopt */
 #define UDP_CSUM_NOXMIT         1