radix-tree: Chain preallocated nodes through ->parent

Chaining through the ->private_data member means we have to zero
->private_data after removing preallocated nodes from the list.
We're about to initialise ->parent anyway, so we can avoid zeroing it.
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>

lib/radix-tree.c

@@ -82,7 +82,7 @@ static struct kmem_cache *radix_tree_node_cachep;
  */
 struct radix_tree_preload {
 	unsigned nr;
-	/* nodes->private_data points to next preallocated node */
+	/* nodes->parent points to next preallocated node */
 	struct radix_tree_node *nodes;
 };
 static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
@@ -405,8 +405,7 @@ radix_tree_node_alloc(gfp_t gfp_mask, struct radix_tree_node *parent,
 		rtp = this_cpu_ptr(&radix_tree_preloads);
 		if (rtp->nr) {
 			ret = rtp->nodes;
-			rtp->nodes = ret->private_data;
-			ret->private_data = NULL;
+			rtp->nodes = ret->parent;
 			rtp->nr--;
 		}
 		/*
@@ -483,7 +482,7 @@ static int __radix_tree_preload(gfp_t gfp_mask, unsigned nr)
 		preempt_disable();
 		rtp = this_cpu_ptr(&radix_tree_preloads);
 		if (rtp->nr < nr) {
-			node->private_data = rtp->nodes;
+			node->parent = rtp->nodes;
 			rtp->nodes = node;
 			rtp->nr++;
 		} else {
@@ -2260,7 +2259,7 @@ static int radix_tree_cpu_dead(unsigned int cpu)
 	rtp = &per_cpu(radix_tree_preloads, cpu);
 	while (rtp->nr) {
 		node = rtp->nodes;
-		rtp->nodes = node->private_data;
+		rtp->nodes = node->parent;
 		kmem_cache_free(radix_tree_node_cachep, node);
 		rtp->nr--;
 	}

tools/testing/radix-tree/linux.c

@@ -35,9 +35,9 @@ void *kmem_cache_alloc(struct kmem_cache *cachep, int flags)
 	if (cachep->nr_objs) {
 		cachep->nr_objs--;
 		node = cachep->objs;
-		cachep->objs = node->private_data;
+		cachep->objs = node->parent;
 		pthread_mutex_unlock(&cachep->lock);
-		node->private_data = NULL;
+		node->parent = NULL;
 	} else {
 		pthread_mutex_unlock(&cachep->lock);
 		node = malloc(cachep->size);
@@ -64,7 +64,7 @@ void kmem_cache_free(struct kmem_cache *cachep, void *objp)
 	} else {
 		struct radix_tree_node *node = objp;
 		cachep->nr_objs++;
-		node->private_data = cachep->objs;
+		node->parent = cachep->objs;
 		cachep->objs = node;
 	}
 	pthread_mutex_unlock(&cachep->lock);