fib_trie: /proc/net/route performance improvement

Use key/offset caching to change /proc/net/route (use by iputils route)
from O(n^2) to O(n). This improves performance from 30sec with 160,000
routes to 1sec.
Signed-off-by: NStephen Hemminger <shemminger@vyatta.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/fib_trie.c

@@ -2459,6 +2459,84 @@ static const struct file_operations fib_trie_fops = {
 	.release = seq_release_net,
 };
 
+struct fib_route_iter {
+	struct seq_net_private p;
+	struct trie *main_trie;
+	loff_t	pos;
+	t_key	key;
+};
+
+static struct leaf *fib_route_get_idx(struct fib_route_iter *iter, loff_t pos)
+{
+	struct leaf *l = NULL;
+	struct trie *t = iter->main_trie;
+
+	/* use cache location of last found key */
+	if (iter->pos > 0 && pos >= iter->pos && (l = fib_find_node(t, iter->key)))
+		pos -= iter->pos;
+	else {
+		iter->pos = 0;
+		l = trie_firstleaf(t);
+	}
+
+	while (l && pos-- > 0) {
+		iter->pos++;
+		l = trie_nextleaf(l);
+	}
+
+	if (l)
+		iter->key = pos;	/* remember it */
+	else
+		iter->pos = 0;		/* forget it */
+
+	return l;
+}
+
+static void *fib_route_seq_start(struct seq_file *seq, loff_t *pos)
+	__acquires(RCU)
+{
+	struct fib_route_iter *iter = seq->private;
+	struct fib_table *tb;
+
+	rcu_read_lock();
+	tb = fib_get_table(iter->p.net, RT_TABLE_MAIN);
+	if (!tb)
+		return NULL;
+
+	iter->main_trie = (struct trie *) tb->tb_data;
+	if (*pos == 0)
+		return SEQ_START_TOKEN;
+	else
+		return fib_route_get_idx(iter, *pos - 1);
+}
+
+static void *fib_route_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	struct fib_route_iter *iter = seq->private;
+	struct leaf *l = v;
+
+	++*pos;
+	if (v == SEQ_START_TOKEN) {
+		iter->pos = 0;
+		l = trie_firstleaf(iter->main_trie);
+	} else {
+		iter->pos++;
+		l = trie_nextleaf(l);
+	}
+
+	if (l)
+		iter->key = l->key;
+	else
+		iter->pos = 0;
+	return l;
+}
+
+static void fib_route_seq_stop(struct seq_file *seq, void *v)
+	__releases(RCU)
+{
+	rcu_read_unlock();
+}
+
 static unsigned fib_flag_trans(int type, __be32 mask, const struct fib_info *fi)
 {
 	static unsigned type2flags[RTN_MAX + 1] = {
@@ -2482,7 +2560,6 @@ static unsigned fib_flag_trans(int type, __be32 mask, const struct fib_info *fi)
  */
 static int fib_route_seq_show(struct seq_file *seq, void *v)
 {
-	const struct fib_trie_iter *iter = seq->private;
 	struct leaf *l = v;
 	struct leaf_info *li;
 	struct hlist_node *node;
@@ -2494,12 +2571,6 @@ static int fib_route_seq_show(struct seq_file *seq, void *v)
 		return 0;
 	}
 
-	if (iter->trie == iter->trie_local)
-		return 0;
-
-	if (IS_TNODE(l))
-		return 0;
-
 	hlist_for_each_entry_rcu(li, node, &l->list, hlist) {
 		struct fib_alias *fa;
 		__be32 mask, prefix;
@@ -2542,16 +2613,16 @@ static int fib_route_seq_show(struct seq_file *seq, void *v)
 }
 
 static const struct seq_operations fib_route_seq_ops = {
-	.start  = fib_trie_seq_start,
-	.next   = fib_trie_seq_next,
-	.stop   = fib_trie_seq_stop,
+	.start  = fib_route_seq_start,
+	.next   = fib_route_seq_next,
+	.stop   = fib_route_seq_stop,
 	.show   = fib_route_seq_show,
 };
 
 static int fib_route_seq_open(struct inode *inode, struct file *file)
 {
 	return seq_open_net(inode, file, &fib_route_seq_ops,
-			    sizeof(struct fib_trie_iter));
+			    sizeof(struct fib_route_iter));
 }
 
 static const struct file_operations fib_route_fops = {