net: bridge: use rhashtable for fdbs

Before this patch the bridge used a fixed 256 element hash table which
was fine for small use cases (in my tests it starts to degrade
above 1000 entries), but it wasn't enough for medium or large
scale deployments. Modern setups have thousands of participants in a
single bridge, even only enabling vlans and adding a few thousand vlan
entries will cause a few thousand fdbs to be automatically inserted per
participating port. So we need to scale the fdb table considerably to
cope with modern workloads, and this patch converts it to use a
rhashtable for its operations thus improving the bridge scalability.
Tests show the following results (10 runs each), at up to 1000 entries
rhashtable is ~3% slower, at 2000 rhashtable is 30% faster, at 3000 it
is 2 times faster and at 30000 it is 50 times faster.
Obviously this happens because of the properties of the two constructs
and is expected, rhashtable keeps pretty much a constant time even with
10000000 entries (tested), while the fixed hash table struggles
considerably even above 10000.
As a side effect this also reduces the net_bridge struct size from 3248
bytes to 1344 bytes. Also note that the key struct is 8 bytes.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/trace/events/bridge.h

@@ -82,8 +82,8 @@ TRACE_EVENT(fdb_delete,
 	TP_fast_assign(
 		__assign_str(br_dev, br->dev->name);
 		__assign_str(dev, f->dst ? f->dst->dev->name : "null");
-		memcpy(__entry->addr, f->addr.addr, ETH_ALEN);
-		__entry->vid = f->vlan_id;
+		memcpy(__entry->addr, f->key.addr.addr, ETH_ALEN);
+		__entry->vid = f->key.vlan_id;
 	),
 
 	TP_printk("br_dev %s dev %s addr %02x:%02x:%02x:%02x:%02x:%02x vid %u",

net/bridge/br_device.c

@@ -125,9 +125,16 @@ static int br_dev_init(struct net_device *dev)
 	if (!br->stats)
 		return -ENOMEM;
 
+	err = br_fdb_hash_init(br);
+	if (err) {
+		free_percpu(br->stats);
+		return err;
+	}
+
 	err = br_vlan_init(br);
 	if (err) {
 		free_percpu(br->stats);
+		br_fdb_hash_fini(br);
 		return err;
 	}
 
@@ -135,6 +142,7 @@ static int br_dev_init(struct net_device *dev)
 	if (err) {
 		free_percpu(br->stats);
 		br_vlan_flush(br);
+		br_fdb_hash_fini(br);
 	}
 	br_set_lockdep_class(dev);
 
@@ -148,6 +156,7 @@ static void br_dev_uninit(struct net_device *dev)
 	br_multicast_dev_del(br);
 	br_multicast_uninit_stats(br);
 	br_vlan_flush(br);
+	br_fdb_hash_fini(br);
 	free_percpu(br->stats);
 }
 
@@ -416,6 +425,7 @@ void br_dev_setup(struct net_device *dev)
 	br->dev = dev;
 	spin_lock_init(&br->lock);
 	INIT_LIST_HEAD(&br->port_list);
+	INIT_HLIST_HEAD(&br->fdb_list);
 	spin_lock_init(&br->hash_lock);
 
 	br->bridge_id.prio[0] = 0x80;

net/bridge/br_private.h

@@ -168,12 +168,17 @@ struct net_bridge_vlan_group {
 	u16				pvid;
 };
 
+struct net_bridge_fdb_key {
+	mac_addr addr;
+	u16 vlan_id;
+};
+
 struct net_bridge_fdb_entry {
-	struct hlist_node		hlist;
+	struct rhash_head		rhnode;
 	struct net_bridge_port		*dst;
 
-	mac_addr			addr;
-	__u16				vlan_id;
+	struct net_bridge_fdb_key	key;
+	struct hlist_node		fdb_node;
 	unsigned char			is_local:1,
 					is_static:1,
 					added_by_user:1,
@@ -315,7 +320,7 @@ struct net_bridge {
 	struct net_bridge_vlan_group	__rcu *vlgrp;
 #endif
 
-	struct hlist_head		hash[BR_HASH_SIZE];
+	struct rhashtable		fdb_hash_tbl;
 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
 	union {
 		struct rtable		fake_rtable;
@@ -405,6 +410,7 @@ struct net_bridge {
 	int offload_fwd_mark;
 #endif
 	bool				neigh_suppress_enabled;
+	struct hlist_head		fdb_list;
 };
 
 struct br_input_skb_cb {
@@ -515,6 +521,8 @@ static inline void br_netpoll_disable(struct net_bridge_port *p)
 /* br_fdb.c */
 int br_fdb_init(void);
 void br_fdb_fini(void);
+int br_fdb_hash_init(struct net_bridge *br);
+void br_fdb_hash_fini(struct net_bridge *br);
 void br_fdb_flush(struct net_bridge *br);
 void br_fdb_find_delete_local(struct net_bridge *br,
 			      const struct net_bridge_port *p,

net/bridge/br_switchdev.c

@@ -121,13 +121,13 @@ br_switchdev_fdb_notify(const struct net_bridge_fdb_entry *fdb, int type)
 
 	switch (type) {
 	case RTM_DELNEIGH:
-		br_switchdev_fdb_call_notifiers(false, fdb->addr.addr,
-						fdb->vlan_id,
+		br_switchdev_fdb_call_notifiers(false, fdb->key.addr.addr,
+						fdb->key.vlan_id,
 						fdb->dst->dev);
 		break;
 	case RTM_NEWNEIGH:
-		br_switchdev_fdb_call_notifiers(true, fdb->addr.addr,
-						fdb->vlan_id,
+		br_switchdev_fdb_call_notifiers(true, fdb->key.addr.addr,
+						fdb->key.vlan_id,
 						fdb->dst->dev);
 		break;
 	}