From: Jesper Dangaard Brouer <[email protected]>
Similar to the IPv4 inet_addr_lst hash table, IPv6 also uses a fixed
256-bucket hash table for address lookups. On hosts with many IPv6
addresses, this results in long hash chains walked under RCU.
The inet6_addr_lst table is used in the route lookup path when no
output interface is specified (oif == 0):
udpv6_sendmsg
ip6_sk_dst_lookup_flow
ip6_dst_lookup_tail
ip6_route_output -> fib6 lookup
__rt6_device_match
ipv6_chk_addr <-- walks inet6_addr_lst
Add CONFIG_INET6_ADDR_HASH_BUCKETS (default 256, range 64-16384, EXPERT)
so hosts with many addresses can size the table appropriately. The value
is rounded up to the nearest power of 2 at compile time via
order_base_2(). Memory cost is one hlist_head pointer per bucket per net
namespace.
Reported-by: Ivan Babrou <[email protected]>
Signed-off-by: Jesper Dangaard Brouer <[email protected]>
---
net/ipv6/Kconfig | 15 +++++++++++++++
net/ipv6/addrconf.c | 2 +-
2 files changed, 16 insertions(+), 1 deletion(-)
diff --git a/net/ipv6/Kconfig b/net/ipv6/Kconfig
index b8f9a8c0302e..963fa0e1a014 100644
--- a/net/ipv6/Kconfig
+++ b/net/ipv6/Kconfig
@@ -238,6 +238,21 @@ config IPV6_FOU_TUNNEL
default NET_FOU_IP_TUNNELS && IPV6_FOU
select IPV6_TUNNEL
+config INET6_ADDR_HASH_BUCKETS
+ int "IPv6 address hash table size" if EXPERT
+ range 64 16384
+ default 256
+ help
+ Number of hash buckets for looking up local IPv6 addresses,
+ e.g. in ipv6_chk_addr() and related callers. Rounded up to
+ the nearest power of 2.
+
+ Hosts with many IPv6 addresses benefit from a larger table to
+ reduce hash chain lengths.
+
+ The default of 256 is fine for most systems. A value of 1024
+ suits hosts with ~500+ addresses.
+
config IPV6_MULTIPLE_TABLES
bool "IPv6: Multiple Routing Tables"
select FIB_RULES
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 0e55f139e05d..dad08f0733ef 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -144,7 +144,7 @@ static int ipv6_generate_stable_address(struct in6_addr
*addr,
u8 dad_count,
const struct inet6_dev *idev);
-#define IN6_ADDR_HSIZE_SHIFT 8
+#define IN6_ADDR_HSIZE_SHIFT order_base_2(CONFIG_INET6_ADDR_HASH_BUCKETS)
#define IN6_ADDR_HSIZE (1 << IN6_ADDR_HSIZE_SHIFT)
static void addrconf_verify(struct net *net);
--
2.43.0
