[PATCH] radix-tree: reduce tree height upon partial truncation

Shrink the height of a radix tree when it is partially truncated - we only do shrinkage of full truncation at present. Signed-off-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>

[PATCH] radix-tree: reduce tree height upon partial truncation
Shrink the height of a radix tree when it is partially truncated - we only do shrinkage of full truncation at present. Signed-off-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Nick Piggin · Linus Torvalds
1 parent d5274261ea
Showing 1 changed file with 36 additions and 10 deletions Side-by-side Diff
lib/radix-tree.c
@@ -253,7 +253,7 @@
 	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
  
 	offset = 0;			/* uninitialised var warning */
-	while (height > 0) {
+	do {
 		if (slot == NULL) {
 			/* Have to add a child node.  */
 			if (!(slot = radix_tree_node_alloc(root)))
  
@@ -271,18 +271,16 @@
 		slot = node->slots[offset];
 		shift -= RADIX_TREE_MAP_SHIFT;
 		height--;
-	}
+	} while (height > 0);
  
 	if (slot != NULL)
 		return -EEXIST;
  
-	if (node) {
-		node->count++;
-		node->slots[offset] = item;
-		BUG_ON(tag_get(node, 0, offset));
-		BUG_ON(tag_get(node, 1, offset));
-	} else
-		root->rnode = item;
+	BUG_ON(!node);
+	node->count++;
+	node->slots[offset] = item;
+	BUG_ON(tag_get(node, 0, offset));
+	BUG_ON(tag_get(node, 1, offset));
  
 	return 0;
 }
@@ -680,6 +678,29 @@
 EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
  
 /**
+ *	radix_tree_shrink    -    shrink height of a radix tree to minimal
+ *	@root		radix tree root
+ */
+static inline void radix_tree_shrink(struct radix_tree_root *root)
+{
+	/* try to shrink tree height */
+	while (root->height > 1 &&
+			root->rnode->count == 1 &&
+			root->rnode->slots[0]) {
+		struct radix_tree_node *to_free = root->rnode;
+
+		root->rnode = to_free->slots[0];
+		root->height--;
+		/* must only free zeroed nodes into the slab */
+		tag_clear(to_free, 0, 0);
+		tag_clear(to_free, 1, 0);
+		to_free->slots[0] = NULL;
+		to_free->count = 0;
+		radix_tree_node_free(to_free);
+	}
+}
+
+/**
  *	radix_tree_delete    -    delete an item from a radix tree
  *	@root:		radix tree root
  *	@index:		index key
  
@@ -755,8 +776,13 @@
 	/* Now free the nodes we do not need anymore */
 	for (pathp = orig_pathp; pathp->node; pathp--) {
 		pathp->node->slots[pathp->offset] = NULL;
-		if (--pathp->node->count)
+		pathp->node->count--;
+
+		if (pathp->node->count) {
+			if (pathp->node == root->rnode)
+				radix_tree_shrink(root);
 			goto out;
+		}
  
 		/* Node with zero slots in use so free it */
 		radix_tree_node_free(pathp->node);
...	...	@@ -253,7 +253,7 @@
253	253	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
254	254
255	255	offset = 0; /* uninitialised var warning */
256		- while (height > 0) {
	256	+ do {
257	257	if (slot == NULL) {
258	258	/* Have to add a child node. */
259	259	if (!(slot = radix_tree_node_alloc(root)))
260	260
...	...	@@ -271,18 +271,16 @@
271	271	slot = node->slots[offset];
272	272	shift -= RADIX_TREE_MAP_SHIFT;
273	273	height--;
274		- }
	274	+ } while (height > 0);
275	275
276	276	if (slot != NULL)
277	277	return -EEXIST;
278	278
279		- if (node) {
280		- node->count++;
281		- node->slots[offset] = item;
282		- BUG_ON(tag_get(node, 0, offset));
283		- BUG_ON(tag_get(node, 1, offset));
284		- } else
285		- root->rnode = item;
	279	+ BUG_ON(!node);
	280	+ node->count++;
	281	+ node->slots[offset] = item;
	282	+ BUG_ON(tag_get(node, 0, offset));
	283	+ BUG_ON(tag_get(node, 1, offset));
286	284
287	285	return 0;
288	286	}
...	...	@@ -680,6 +678,29 @@
680	678	EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
681	679
682	680	/**
	681	+ * radix_tree_shrink - shrink height of a radix tree to minimal
	682	+ * @root radix tree root
	683	+ */
	684	+static inline void radix_tree_shrink(struct radix_tree_root *root)
	685	+{
	686	+ /* try to shrink tree height */
	687	+ while (root->height > 1 &&
	688	+ root->rnode->count == 1 &&
	689	+ root->rnode->slots[0]) {
	690	+ struct radix_tree_node *to_free = root->rnode;
	691	+
	692	+ root->rnode = to_free->slots[0];
	693	+ root->height--;
	694	+ /* must only free zeroed nodes into the slab */
	695	+ tag_clear(to_free, 0, 0);
	696	+ tag_clear(to_free, 1, 0);
	697	+ to_free->slots[0] = NULL;
	698	+ to_free->count = 0;
	699	+ radix_tree_node_free(to_free);
	700	+ }
	701	+}
	702	+
	703	+/**
683	704	* radix_tree_delete - delete an item from a radix tree
684	705	* @root: radix tree root
685	706	* @index: index key
686	707
...	...	@@ -755,8 +776,13 @@
755	776	/* Now free the nodes we do not need anymore */
756	777	for (pathp = orig_pathp; pathp->node; pathp--) {
757	778	pathp->node->slots[pathp->offset] = NULL;
758		- if (--pathp->node->count)
	779	+ pathp->node->count--;
	780	+
	781	+ if (pathp->node->count) {
	782	+ if (pathp->node == root->rnode)
	783	+ radix_tree_shrink(root);
759	784	goto out;
	785	+ }
760	786
761	787	/* Node with zero slots in use so free it */
762	788	radix_tree_node_free(pathp->node);