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

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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>
This commit is contained in:
Nick Piggin 2006-01-08 01:01:41 -08:00 committed by Linus Torvalds
parent d5274261ea
commit a5f51c9667
1 changed files with 36 additions and 10 deletions
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46
lib/radix-tree.c
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@ -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) {
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;
}
@ -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);