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/net/ipv6/udp.c b/net/ipv6/udp.c
index c6a303ec834c..ff778c172ef2 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -132,7 +132,7 @@ static struct sock *__udp6_lib_lookup(struct net *net,
         struct sock *sk, *result;
         struct hlist_nulls_node *node;
         unsigned short hnum = ntohs(dport);
-        unsigned int hash = udp_hashfn(net, hnum);
+        unsigned int hash = udp_hashfn(net, hnum, udptable->mask);
         struct udp_hslot *hslot = &udptable->hash[hash];
         int score, badness;
 
@@ -452,7 +452,7 @@ static int __udp6_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
 {
         struct sock *sk, *sk2;
         const struct udphdr *uh = udp_hdr(skb);
-        struct udp_hslot *hslot = &udptable->hash[udp_hashfn(net, ntohs(uh->dest))];
+        struct udp_hslot *hslot = udp_hashslot(udptable, net, ntohs(uh->dest));
         int dif;
 
         spin_lock(&hslot->lock);
@@ -1197,7 +1197,7 @@ static void udp6_sock_seq_show(struct seq_file *seq, struct sock *sp, int bucket
         destp = ntohs(inet->dport);
         srcp  = ntohs(inet->sport);
         seq_printf(seq,
-                   "%4d: %08X%08X%08X%08X:%04X %08X%08X%08X%08X:%04X "
+                   "%5d: %08X%08X%08X%08X:%04X %08X%08X%08X%08X:%04X "
                    "%02X %08X:%08X %02X:%08lX %08X %5d %8d %lu %d %p %d\n",
                    bucket,
                    src->s6_addr32[0], src->s6_addr32[1],