IPV4: fib_trie use vmalloc for large tnodes

Use vmalloc rather than alloc_pages to avoid wasting memory.
The problem is that tnode structure has a power of 2 sized array,
plus a header. So the current code wastes almost half the memory
allocated because it always needs the next bigger size to hold
that small header.

This is similar to an earlier patch by Eric, but instead of a list
and lock, I used a workqueue to handle the fact that vfree can't
be done in interrupt context.
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_trie.c

@@ -122,7 +122,10 @@ struct tnode {
 	unsigned char bits;		/* 2log(KEYLENGTH) bits needed */
 	unsigned int full_children;	/* KEYLENGTH bits needed */
 	unsigned int empty_children;	/* KEYLENGTH bits needed */
-	struct rcu_head rcu;
+	union {
+		struct rcu_head rcu;
+		struct work_struct work;
+	};
 	struct node *child[0];
 };
 
@@ -346,16 +349,16 @@ static inline void free_leaf_info(struct leaf_info *leaf)
 
 static struct tnode *tnode_alloc(size_t size)
 {
-	struct page *pages;
-
 	if (size <= PAGE_SIZE)
 		return kzalloc(size, GFP_KERNEL);
+	else
+		return __vmalloc(size, GFP_KERNEL | __GFP_ZERO, PAGE_KERNEL);
+}
 
-	pages = alloc_pages(GFP_KERNEL|__GFP_ZERO, get_order(size));
-	if (!pages)
-		return NULL;
-
-	return page_address(pages);
+static void __tnode_vfree(struct work_struct *arg)
+{
+	struct tnode *tn = container_of(arg, struct tnode, work);
+	vfree(tn);
 }
 
 static void __tnode_free_rcu(struct rcu_head *head)
@@ -366,8 +369,10 @@ static void __tnode_free_rcu(struct rcu_head *head)
 
 	if (size <= PAGE_SIZE)
 		kfree(tn);
-	else
-		free_pages((unsigned long)tn, get_order(size));
+	else {
+		INIT_WORK(&tn->work, __tnode_vfree);
+		schedule_work(&tn->work);
+	}
 }
 
 static inline void tnode_free(struct tnode *tn)