fib_trie: move leaf and tnode to occupy the same spot in the key vector

If we are going to compact the leaf and tnode we first need to make sure
the fields are all in the same place.  In that regard I am moving the leaf
pointer which represents the fib_alias hash list to occupy what is
currently the first key_vector pointer.
Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_trie.c

@@ -94,24 +94,27 @@ typedef unsigned int t_key;
 #define get_index(_key, _kv) (((_key) ^ (_kv)->key) >> (_kv)->pos)
 
 struct tnode {
+	struct rcu_head rcu;
+
+	t_key empty_children; /* KEYLENGTH bits needed */
+	t_key full_children;  /* KEYLENGTH bits needed */
+	struct tnode __rcu *parent;
+
 	t_key key;
-	unsigned char bits;		/* 2log(KEYLENGTH) bits needed */
 	unsigned char pos;		/* 2log(KEYLENGTH) bits needed */
+	unsigned char bits;		/* 2log(KEYLENGTH) bits needed */
 	unsigned char slen;
-	struct tnode __rcu *parent;
-	struct rcu_head rcu;
 	union {
-		/* The fields in this struct are valid if bits > 0 (TNODE) */
-		struct {
-			t_key empty_children; /* KEYLENGTH bits needed */
-			t_key full_children;  /* KEYLENGTH bits needed */
-			struct tnode __rcu *child[0];
-		};
-		/* This list pointer if valid if bits == 0 (LEAF) */
+		/* This list pointer if valid if (pos | bits) == 0 (LEAF) */
 		struct hlist_head leaf;
+		/* This array is valid if (pos | bits) > 0 (TNODE) */
+		struct tnode __rcu *tnode[0];
 	};
 };
 
+#define TNODE_SIZE(n)	offsetof(struct tnode, tnode[n])
+#define LEAF_SIZE	TNODE_SIZE(1)
+
 #ifdef CONFIG_IP_FIB_TRIE_STATS
 struct trie_use_stats {
 	unsigned int gets;
@@ -180,14 +183,14 @@ static inline unsigned long tnode_child_length(const struct tnode *tn)
 static inline struct tnode *tnode_get_child(const struct tnode *tn,
 					    unsigned long i)
 {
-	return rtnl_dereference(tn->child[i]);
+	return rtnl_dereference(tn->tnode[i]);
 }
 
 /* caller must hold RCU read lock or RTNL */
 static inline struct tnode *tnode_get_child_rcu(const struct tnode *tn,
 						unsigned long i)
 {
-	return rcu_dereference_rtnl(tn->child[i]);
+	return rcu_dereference_rtnl(tn->tnode[i]);
 }
 
 /* To understand this stuff, an understanding of keys and all their bits is
@@ -266,7 +269,7 @@ static inline void alias_free_mem_rcu(struct fib_alias *fa)
 }
 
 #define TNODE_KMALLOC_MAX \
-	ilog2((PAGE_SIZE - sizeof(struct tnode)) / sizeof(struct tnode *))
+	ilog2((PAGE_SIZE - TNODE_SIZE(0)) / sizeof(struct tnode *))
 
 static void __node_free_rcu(struct rcu_head *head)
 {
@@ -324,7 +327,7 @@ static struct tnode *leaf_new(t_key key, struct fib_alias *fa)
 
 static struct tnode *tnode_new(t_key key, int pos, int bits)
 {
-	size_t sz = offsetof(struct tnode, child[1ul << bits]);
+	size_t sz = TNODE_SIZE(1ul << bits);
 	struct tnode *tn = tnode_alloc(sz);
 	unsigned int shift = pos + bits;
 
@@ -343,7 +346,7 @@ static struct tnode *tnode_new(t_key key, int pos, int bits)
 			tn->empty_children = 1ul << bits;
 	}
 
-	pr_debug("AT %p s=%zu %zu\n", tn, sizeof(struct tnode),
+	pr_debug("AT %p s=%zu %zu\n", tn, TNODE_SIZE(0),
 		 sizeof(struct tnode *) << bits);
 	return tn;
 }
@@ -384,7 +387,7 @@ static void put_child(struct tnode *tn, unsigned long i, struct tnode *n)
 	if (n && (tn->slen < n->slen))
 		tn->slen = n->slen;
 
-	rcu_assign_pointer(tn->child[i], n);
+	rcu_assign_pointer(tn->tnode[i], n);
 }
 
 static void update_children(struct tnode *tn)
@@ -435,7 +438,7 @@ static void tnode_free(struct tnode *tn)
 
 	while (head) {
 		head = head->next;
-		tnode_free_size += offsetof(struct tnode, child[1 << tn->bits]);
+		tnode_free_size += TNODE_SIZE(1ul << tn->bits);
 		node_free(tn);
 
 		tn = container_of(head, struct tnode, rcu);
@@ -788,7 +791,7 @@ static void resize(struct trie *t, struct tnode *tn)
 	 * doing it ourselves.  This way we can let RCU fully do its
 	 * thing without us interfering
 	 */
-	cptr = tp ? &tp->child[get_index(tn->key, tp)] : &t->trie;
+	cptr = tp ? &tp->tnode[get_index(tn->key, tp)] : &t->trie;
 	BUG_ON(tn != rtnl_dereference(*cptr));
 
 	/* Double as long as the resulting node has a number of
@@ -1241,7 +1244,7 @@ int fib_table_lookup(struct fib_table *tb, const struct flowi4 *flp,
 	/* Step 2: Sort out leaves and begin backtracing for longest prefix */
 	for (;;) {
 		/* record the pointer where our next node pointer is stored */
-		struct tnode __rcu **cptr = n->child;
+		struct tnode __rcu **cptr = n->tnode;
 
 		/* This test verifies that none of the bits that differ
 		 * between the key and the prefix exist in the region of
@@ -1287,7 +1290,7 @@ int fib_table_lookup(struct fib_table *tb, const struct flowi4 *flp,
 			cindex &= cindex - 1;
 
 			/* grab pointer for next child node */
-			cptr = &pn->child[cindex];
+			cptr = &pn->tnode[cindex];
 		}
 	}
 
@@ -1685,7 +1688,7 @@ void __init fib_trie_init(void)
 					  0, SLAB_PANIC, NULL);
 
 	trie_leaf_kmem = kmem_cache_create("ip_fib_trie",
-					   sizeof(struct tnode),
+					   LEAF_SIZE,
 					   0, SLAB_PANIC, NULL);
 }
 
@@ -1843,13 +1846,13 @@ static void trie_show_stats(struct seq_file *seq, struct trie_stat *stat)
 	seq_printf(seq, "\tMax depth:      %u\n", stat->maxdepth);
 
 	seq_printf(seq, "\tLeaves:         %u\n", stat->leaves);
-	bytes = sizeof(struct tnode) * stat->leaves;
+	bytes = LEAF_SIZE * stat->leaves;
 
 	seq_printf(seq, "\tPrefixes:       %u\n", stat->prefixes);
 	bytes += sizeof(struct fib_alias) * stat->prefixes;
 
 	seq_printf(seq, "\tInternal nodes: %u\n\t", stat->tnodes);
-	bytes += sizeof(struct tnode) * stat->tnodes;
+	bytes += TNODE_SIZE(0) * stat->tnodes;
 
 	max = MAX_STAT_DEPTH;
 	while (max > 0 && stat->nodesizes[max-1] == 0)
@@ -1918,7 +1921,7 @@ static int fib_triestat_seq_show(struct seq_file *seq, void *v)
 	seq_printf(seq,
 		   "Basic info: size of leaf:"
 		   " %Zd bytes, size of tnode: %Zd bytes.\n",
-		   sizeof(struct tnode), sizeof(struct tnode));
+		   LEAF_SIZE, TNODE_SIZE(0));
 
 	for (h = 0; h < FIB_TABLE_HASHSZ; h++) {
 		struct hlist_head *head = &net->ipv4.fib_table_hash[h];