openwrt/target/linux/generic/patches-3.18/080-03-fib_trie-Make-leaf-and-tnode-more-uniform.patch

From: Alexander Duyck <alexander.h.duyck@redhat.com>
Date: Wed, 31 Dec 2014 10:55:35 -0800
Subject: [PATCH] fib_trie: Make leaf and tnode more uniform

This change makes some fundamental changes to the way leaves and tnodes are
constructed.  The big differences are:
1.  Leaves now populate pos and bits indicating their full key size.
2.  Trie nodes now mask out their lower bits to be consistent with the leaf
3.  Both structures have been reordered so that rt_trie_node now consisists
    of a much larger region including the pos, bits, and rcu portions of
    the tnode structure.

On 32b systems this will result in the leaf being 4B larger as the pos and
bits values were added to a hole created by the key as it was only 4B in
length.

Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -87,24 +87,38 @@
 
 typedef unsigned int t_key;
 
-#define T_TNODE 0
-#define T_LEAF  1
-#define NODE_TYPE_MASK	0x1UL
-#define NODE_TYPE(node) ((node)->parent & NODE_TYPE_MASK)
+#define IS_TNODE(n) ((n)->bits)
+#define IS_LEAF(n) (!(n)->bits)
 
-#define IS_TNODE(n) (!(n->parent & T_LEAF))
-#define IS_LEAF(n) (n->parent & T_LEAF)
+struct tnode {
+	t_key key;
+	unsigned char bits;		/* 2log(KEYLENGTH) bits needed */
+	unsigned char pos;		/* 2log(KEYLENGTH) bits needed */
+	struct tnode __rcu *parent;
+	union {
+		struct rcu_head rcu;
+		struct tnode *tnode_free;
+	};
+	unsigned int full_children;	/* KEYLENGTH bits needed */
+	unsigned int empty_children;	/* KEYLENGTH bits needed */
+	struct rt_trie_node __rcu *child[0];
+};
 
 struct rt_trie_node {
-	unsigned long parent;
 	t_key key;
+	unsigned char bits;
+	unsigned char pos;
+	struct tnode __rcu *parent;
+	struct rcu_head rcu;
 };
 
 struct leaf {
-	unsigned long parent;
 	t_key key;
-	struct hlist_head list;
+	unsigned char bits;
+	unsigned char pos;
+	struct tnode __rcu *parent;
 	struct rcu_head rcu;
+	struct hlist_head list;
 };
 
 struct leaf_info {
@@ -115,20 +129,6 @@ struct leaf_info {
 	struct rcu_head rcu;
 };
 
-struct tnode {
-	unsigned long parent;
-	t_key key;
-	unsigned char pos;		/* 2log(KEYLENGTH) bits needed */
-	unsigned char bits;		/* 2log(KEYLENGTH) bits needed */
-	unsigned int full_children;	/* KEYLENGTH bits needed */
-	unsigned int empty_children;	/* KEYLENGTH bits needed */
-	union {
-		struct rcu_head rcu;
-		struct tnode *tnode_free;
-	};
-	struct rt_trie_node __rcu *child[0];
-};
-
 #ifdef CONFIG_IP_FIB_TRIE_STATS
 struct trie_use_stats {
 	unsigned int gets;
@@ -176,38 +176,27 @@ static const int sync_pages = 128;
 static struct kmem_cache *fn_alias_kmem __read_mostly;
 static struct kmem_cache *trie_leaf_kmem __read_mostly;
 
-/*
- * caller must hold RTNL
- */
-static inline struct tnode *node_parent(const struct rt_trie_node *node)
-{
-	unsigned long parent;
+/* caller must hold RTNL */
+#define node_parent(n) rtnl_dereference((n)->parent)
 
-	parent = rcu_dereference_index_check(node->parent, lockdep_rtnl_is_held());
+/* caller must hold RCU read lock or RTNL */
+#define node_parent_rcu(n) rcu_dereference_rtnl((n)->parent)
 
-	return (struct tnode *)(parent & ~NODE_TYPE_MASK);
-}
-
-/*
- * caller must hold RCU read lock or RTNL
- */
-static inline struct tnode *node_parent_rcu(const struct rt_trie_node *node)
+/* wrapper for rcu_assign_pointer */
+static inline void node_set_parent(struct rt_trie_node *node, struct tnode *ptr)
 {
-	unsigned long parent;
-
-	parent = rcu_dereference_index_check(node->parent, rcu_read_lock_held() ||
-							   lockdep_rtnl_is_held());
-
-	return (struct tnode *)(parent & ~NODE_TYPE_MASK);
+	if (node)
+		rcu_assign_pointer(node->parent, ptr);
 }
 
-/* Same as rcu_assign_pointer
- * but that macro() assumes that value is a pointer.
+#define NODE_INIT_PARENT(n, p) RCU_INIT_POINTER((n)->parent, p)
+
+/* This provides us with the number of children in this node, in the case of a
+ * leaf this will return 0 meaning none of the children are accessible.
  */
-static inline void node_set_parent(struct rt_trie_node *node, struct tnode *ptr)
+static inline int tnode_child_length(const struct tnode *tn)
 {
-	smp_wmb();
-	node->parent = (unsigned long)ptr | NODE_TYPE(node);
+	return (1ul << tn->bits) & ~(1ul);
 }
 
 /*
@@ -215,7 +204,7 @@ static inline void node_set_parent(struc
  */
 static inline struct rt_trie_node *tnode_get_child(const struct tnode *tn, unsigned int i)
 {
-	BUG_ON(i >= 1U << tn->bits);
+	BUG_ON(i >= tnode_child_length(tn));
 
 	return rtnl_dereference(tn->child[i]);
 }
@@ -225,16 +214,11 @@ static inline struct rt_trie_node *tnode
  */
 static inline struct rt_trie_node *tnode_get_child_rcu(const struct tnode *tn, unsigned int i)
 {
-	BUG_ON(i >= 1U << tn->bits);
+	BUG_ON(i >= tnode_child_length(tn));
 
 	return rcu_dereference_rtnl(tn->child[i]);
 }
 
-static inline int tnode_child_length(const struct tnode *tn)
-{
-	return 1 << tn->bits;
-}
-
 static inline t_key mask_pfx(t_key k, unsigned int l)
 {
 	return (l == 0) ? 0 : k >> (KEYLENGTH-l) << (KEYLENGTH-l);
@@ -336,11 +320,6 @@ static inline int tkey_mismatch(t_key a,
 
 */
 
-static inline void check_tnode(const struct tnode *tn)
-{
-	WARN_ON(tn && tn->pos+tn->bits > 32);
-}
-
 static const int halve_threshold = 25;
 static const int inflate_threshold = 50;
 static const int halve_threshold_root = 15;
@@ -426,11 +405,20 @@ static void tnode_free_flush(void)
 	}
 }
 
-static struct leaf *leaf_new(void)
+static struct leaf *leaf_new(t_key key)
 {
 	struct leaf *l = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
 	if (l) {
-		l->parent = T_LEAF;
+		l->parent = NULL;
+		/* set key and pos to reflect full key value
+		 * any trailing zeros in the key should be ignored
+		 * as the nodes are searched
+		 */
+		l->key = key;
+		l->pos = KEYLENGTH;
+		/* set bits to 0 indicating we are not a tnode */
+		l->bits = 0;
+
 		INIT_HLIST_HEAD(&l->list);
 	}
 	return l;
@@ -451,12 +439,16 @@ static struct tnode *tnode_new(t_key key
 {
 	size_t sz = sizeof(struct tnode) + (sizeof(struct rt_trie_node *) << bits);
 	struct tnode *tn = tnode_alloc(sz);
+	unsigned int shift = pos + bits;
+
+	/* verify bits and pos their msb bits clear and values are valid */
+	BUG_ON(!bits || (shift > KEYLENGTH));
 
 	if (tn) {
-		tn->parent = T_TNODE;
+		tn->parent = NULL;
 		tn->pos = pos;
 		tn->bits = bits;
-		tn->key = key;
+		tn->key = mask_pfx(key, pos);
 		tn->full_children = 0;
 		tn->empty_children = 1<<bits;
 	}
@@ -473,10 +465,7 @@ static struct tnode *tnode_new(t_key key
 
 static inline int tnode_full(const struct tnode *tn, const struct rt_trie_node *n)
 {
-	if (n == NULL || IS_LEAF(n))
-		return 0;
-
-	return ((struct tnode *) n)->pos == tn->pos + tn->bits;
+	return n && IS_TNODE(n) && (n->pos == (tn->pos + tn->bits));
 }
 
 static inline void put_child(struct tnode *tn, int i,
@@ -514,8 +503,7 @@ static void tnode_put_child_reorg(struct
 	else if (!wasfull && isfull)
 		tn->full_children++;
 
-	if (n)
-		node_set_parent(n, tn);
+	node_set_parent(n, tn);
 
 	rcu_assign_pointer(tn->child[i], n);
 }
@@ -523,7 +511,7 @@ static void tnode_put_child_reorg(struct
 #define MAX_WORK 10
 static struct rt_trie_node *resize(struct trie *t, struct tnode *tn)
 {
-	int i;
+	struct rt_trie_node *n = NULL;
 	struct tnode *old_tn;
 	int inflate_threshold_use;
 	int halve_threshold_use;
@@ -536,12 +524,11 @@ static struct rt_trie_node *resize(struc
 		 tn, inflate_threshold, halve_threshold);
 
 	/* No children */
-	if (tn->empty_children == tnode_child_length(tn)) {
-		tnode_free_safe(tn);
-		return NULL;
-	}
+	if (tn->empty_children > (tnode_child_length(tn) - 1))
+		goto no_children;
+
 	/* One child */
-	if (tn->empty_children == tnode_child_length(tn) - 1)
+	if (tn->empty_children == (tnode_child_length(tn) - 1))
 		goto one_child;
 	/*
 	 * Double as long as the resulting node has a number of
@@ -607,11 +594,9 @@ static struct rt_trie_node *resize(struc
 	 *
 	 */
 
-	check_tnode(tn);
-
 	/* Keep root node larger  */
 
-	if (!node_parent((struct rt_trie_node *)tn)) {
+	if (!node_parent(tn)) {
 		inflate_threshold_use = inflate_threshold_root;
 		halve_threshold_use = halve_threshold_root;
 	} else {
@@ -637,8 +622,6 @@ static struct rt_trie_node *resize(struc
 		}
 	}
 
-	check_tnode(tn);
-
 	/* Return if at least one inflate is run */
 	if (max_work != MAX_WORK)
 		return (struct rt_trie_node *) tn;
@@ -666,21 +649,16 @@ static struct rt_trie_node *resize(struc
 
 
 	/* Only one child remains */
-	if (tn->empty_children == tnode_child_length(tn) - 1) {
+	if (tn->empty_children == (tnode_child_length(tn) - 1)) {
+		unsigned long i;
 one_child:
-		for (i = 0; i < tnode_child_length(tn); i++) {
-			struct rt_trie_node *n;
-
-			n = rtnl_dereference(tn->child[i]);
-			if (!n)
-				continue;
-
-			/* compress one level */
-
-			node_set_parent(n, NULL);
-			tnode_free_safe(tn);
-			return n;
-		}
+		for (i = tnode_child_length(tn); !n && i;)
+			n = tnode_get_child(tn, --i);
+no_children:
+		/* compress one level */
+		node_set_parent(n, NULL);
+		tnode_free_safe(tn);
+		return n;
 	}
 	return (struct rt_trie_node *) tn;
 }
@@ -760,8 +738,7 @@ static struct tnode *inflate(struct trie
 
 		/* A leaf or an internal node with skipped bits */
 
-		if (IS_LEAF(node) || ((struct tnode *) node)->pos >
-		   tn->pos + tn->bits - 1) {
+		if (IS_LEAF(node) || (node->pos > (tn->pos + tn->bits - 1))) {
 			put_child(tn,
 				tkey_extract_bits(node->key, oldtnode->pos, oldtnode->bits + 1),
 				node);
@@ -958,11 +935,9 @@ fib_find_node(struct trie *t, u32 key)
 	pos = 0;
 	n = rcu_dereference_rtnl(t->trie);
 
-	while (n != NULL &&  NODE_TYPE(n) == T_TNODE) {
+	while (n && IS_TNODE(n)) {
 		tn = (struct tnode *) n;
 
-		check_tnode(tn);
-
 		if (tkey_sub_equals(tn->key, pos, tn->pos-pos, key)) {
 			pos = tn->pos + tn->bits;
 			n = tnode_get_child_rcu(tn,
@@ -988,7 +963,7 @@ static void trie_rebalance(struct trie *
 
 	key = tn->key;
 
-	while (tn != NULL && (tp = node_parent((struct rt_trie_node *)tn)) != NULL) {
+	while (tn != NULL && (tp = node_parent(tn)) != NULL) {
 		cindex = tkey_extract_bits(key, tp->pos, tp->bits);
 		wasfull = tnode_full(tp, tnode_get_child(tp, cindex));
 		tn = (struct tnode *)resize(t, tn);
@@ -996,7 +971,7 @@ static void trie_rebalance(struct trie *
 		tnode_put_child_reorg(tp, cindex,
 				      (struct rt_trie_node *)tn, wasfull);
 
-		tp = node_parent((struct rt_trie_node *) tn);
+		tp = node_parent(tn);
 		if (!tp)
 			rcu_assign_pointer(t->trie, (struct rt_trie_node *)tn);
 
@@ -1048,11 +1023,9 @@ static struct list_head *fib_insert_node
 	 * If it doesn't, we need to replace it with a T_TNODE.
 	 */
 
-	while (n != NULL &&  NODE_TYPE(n) == T_TNODE) {
+	while (n && IS_TNODE(n)) {
 		tn = (struct tnode *) n;
 
-		check_tnode(tn);
-
 		if (tkey_sub_equals(tn->key, pos, tn->pos-pos, key)) {
 			tp = tn;
 			pos = tn->pos + tn->bits;
@@ -1087,12 +1060,11 @@ static struct list_head *fib_insert_node
 		insert_leaf_info(&l->list, li);
 		goto done;
 	}
-	l = leaf_new();
+	l = leaf_new(key);
 
 	if (!l)
 		return NULL;
 
-	l->key = key;
 	li = leaf_info_new(plen);
 
 	if (!li) {
@@ -1569,7 +1541,7 @@ backtrace:
 		if (chopped_off <= pn->bits) {
 			cindex &= ~(1 << (chopped_off-1));
 		} else {
-			struct tnode *parent = node_parent_rcu((struct rt_trie_node *) pn);
+			struct tnode *parent = node_parent_rcu(pn);
 			if (!parent)
 				goto failed;
 
@@ -1597,7 +1569,7 @@ EXPORT_SYMBOL_GPL(fib_table_lookup);
  */
 static void trie_leaf_remove(struct trie *t, struct leaf *l)
 {
-	struct tnode *tp = node_parent((struct rt_trie_node *) l);
+	struct tnode *tp = node_parent(l);
 
 	pr_debug("entering trie_leaf_remove(%p)\n", l);
 
@@ -2374,7 +2346,7 @@ static int fib_trie_seq_show(struct seq_
 
 	if (IS_TNODE(n)) {
 		struct tnode *tn = (struct tnode *) n;
-		__be32 prf = htonl(mask_pfx(tn->key, tn->pos));
+		__be32 prf = htonl(tn->key);
 
 		seq_indent(seq, iter->depth-1);
 		seq_printf(seq, "  +-- %pI4/%d %d %d %d\n",