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Commit a5f51c96 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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[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: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent d5274261

lib/radix-tree.c

+36 −10
Original line number Diff line number Diff line
@@ -253,7 +253,7 @@ int radix_tree_insert(struct radix_tree_root *root, 
	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 @@ int radix_tree_insert(struct radix_tree_root *root, 
		slot = node->slots[offset];

		shift -= RADIX_TREE_MAP_SHIFT;

		height--;

	}

	} while (height > 0);



	if (slot != NULL)

		return -EEXIST;



	if (node) {

	BUG_ON(!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;



	return 0;

}
@@ -679,6 +677,29 @@ radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results, 
}

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
@@ -755,8 +776,13 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index) 
	/* 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);