[PATCH] radix-tree: Remove unnecessary indirections and clean up code

- There is frequent use of indirections in the radix code. This patch
  removes those indirections, makes the code more readable and allows
  the compilers to generate better code.

- Removing indirections allows the removal of several casts.

- Removing indirections allows the reduction of the radix_tree_path
  size from 3 to 2 words.

- Use pathp-> consistently.

- Remove unnecessary tmp variable in radix_tree_insert

- Separate the upper layer processing from the lowest layer in __lookup()
  in order to make it easier to understand what is going on and allow
  compilers to generate better code for the loop.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: James Bottomley <James.Bottomley@steeleye.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

lib/radix-tree.c

 /*
  * Copyright (C) 2001 Momchil Velikov
  * Portions Copyright (C) 2001 Christoph Hellwig
+ * Copyright (C) 2005 SGI, Christoph Lameter <clameter@sgi.com>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -51,7 +52,7 @@ struct radix_tree_node {
 };
 
 struct radix_tree_path {
-	struct radix_tree_node *node, **slot;
+	struct radix_tree_node *node;
 	int offset;
 };
 
@@ -227,7 +228,7 @@ static int radix_tree_extend(struct radix_tree_root *root, unsigned long index)
 int radix_tree_insert(struct radix_tree_root *root,
 			unsigned long index, void *item)
 {
-	struct radix_tree_node *node = NULL, *tmp, **slot;
+	struct radix_tree_node *node = NULL, *slot;
 	unsigned int height, shift;
 	int offset;
 	int error;
@@ -240,38 +241,42 @@ int radix_tree_insert(struct radix_tree_root *root,
 			return error;
 	}
 
-	slot = &root->rnode;
+	slot = root->rnode;
 	height = root->height;
 	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
 
 	offset = 0;			/* uninitialised var warning */
 	while (height > 0) {
-		if (*slot == NULL) {
+		if (slot == NULL) {
 			/* Have to add a child node.  */
-			if (!(tmp = radix_tree_node_alloc(root)))
+			if (!(slot = radix_tree_node_alloc(root)))
 				return -ENOMEM;
-			*slot = tmp;
-			if (node)
+			if (node) {
+				node->slots[offset] = slot;
 				node->count++;
+			} else
+				root->rnode = slot;
 		}
 
 		/* Go a level down */
 		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
-		node = *slot;
-		slot = (struct radix_tree_node **)(node->slots + offset);
+		node = slot;
+		slot = node->slots[offset];
 		shift -= RADIX_TREE_MAP_SHIFT;
 		height--;
 	}
 
-	if (*slot != NULL)
+	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;
 
-	*slot = item;
 	return 0;
 }
 EXPORT_SYMBOL(radix_tree_insert);
@@ -286,27 +291,25 @@ EXPORT_SYMBOL(radix_tree_insert);
 void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
 {
 	unsigned int height, shift;
-	struct radix_tree_node **slot;
+	struct radix_tree_node *slot;
 
 	height = root->height;
 	if (index > radix_tree_maxindex(height))
 		return NULL;
 
 	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
-	slot = &root->rnode;
+	slot = root->rnode;
 
 	while (height > 0) {
-		if (*slot == NULL)
+		if (slot == NULL)
 			return NULL;
 
-		slot = (struct radix_tree_node **)
-			((*slot)->slots +
-				((index >> shift) & RADIX_TREE_MAP_MASK));
+		slot = slot->slots[(index >> shift) & RADIX_TREE_MAP_MASK];
 		shift -= RADIX_TREE_MAP_SHIFT;
 		height--;
 	}
 
-	return *slot;
+	return slot;
 }
 EXPORT_SYMBOL(radix_tree_lookup);
 
@@ -326,27 +329,27 @@ void *radix_tree_tag_set(struct radix_tree_root *root,
 			unsigned long index, int tag)
 {
 	unsigned int height, shift;
-	struct radix_tree_node **slot;
+	struct radix_tree_node *slot;
 
 	height = root->height;
 	if (index > radix_tree_maxindex(height))
 		return NULL;
 
 	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
-	slot = &root->rnode;
+	slot = root->rnode;
 
 	while (height > 0) {
 		int offset;
 
 		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
-		tag_set(*slot, tag, offset);
-		slot = (struct radix_tree_node **)((*slot)->slots + offset);
-		BUG_ON(*slot == NULL);
+		tag_set(slot, tag, offset);
+		slot = slot->slots[offset];
+		BUG_ON(slot == NULL);
 		shift -= RADIX_TREE_MAP_SHIFT;
 		height--;
 	}
 
-	return *slot;
+	return slot;
 }
 EXPORT_SYMBOL(radix_tree_tag_set);
 
@@ -367,6 +370,7 @@ void *radix_tree_tag_clear(struct radix_tree_root *root,
 			unsigned long index, int tag)
 {
 	struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;
+	struct radix_tree_node *slot;
 	unsigned int height, shift;
 	void *ret = NULL;
 
@@ -376,38 +380,37 @@ void *radix_tree_tag_clear(struct radix_tree_root *root,
 
 	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 	pathp->node = NULL;
-	pathp->slot = &root->rnode;
+	slot = root->rnode;
 
 	while (height > 0) {
 		int offset;
 
-		if (*pathp->slot == NULL)
+		if (slot == NULL)
 			goto out;
 
 		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 		pathp[1].offset = offset;
-		pathp[1].node = *pathp[0].slot;
-		pathp[1].slot = (struct radix_tree_node **)
-				(pathp[1].node->slots + offset);
+		pathp[1].node = slot;
+		slot = slot->slots[offset];
 		pathp++;
 		shift -= RADIX_TREE_MAP_SHIFT;
 		height--;
 	}
 
-	ret = *pathp[0].slot;
+	ret = slot;
 	if (ret == NULL)
 		goto out;
 
 	do {
 		int idx;
 
-		tag_clear(pathp[0].node, tag, pathp[0].offset);
+		tag_clear(pathp->node, tag, pathp->offset);
 		for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
-			if (pathp[0].node->tags[tag][idx])
+			if (pathp->node->tags[tag][idx])
 				goto out;
 		}
 		pathp--;
-	} while (pathp[0].node);
+	} while (pathp->node);
 out:
 	return ret;
 }
@@ -429,7 +432,7 @@ int radix_tree_tag_get(struct radix_tree_root *root,
 			unsigned long index, int tag)
 {
 	unsigned int height, shift;
-	struct radix_tree_node **slot;
+	struct radix_tree_node *slot;
 	int saw_unset_tag = 0;
 
 	height = root->height;
@@ -437,12 +440,12 @@ int radix_tree_tag_get(struct radix_tree_root *root,
 		return 0;
 
 	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
-	slot = &root->rnode;
+	slot = root->rnode;
 
 	for ( ; ; ) {
 		int offset;
 
-		if (*slot == NULL)
+		if (slot == NULL)
 			return 0;
 
 		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
@@ -451,15 +454,15 @@ int radix_tree_tag_get(struct radix_tree_root *root,
 		 * This is just a debug check.  Later, we can bale as soon as
 		 * we see an unset tag.
 		 */
-		if (!tag_get(*slot, tag, offset))
+		if (!tag_get(slot, tag, offset))
 			saw_unset_tag = 1;
 		if (height == 1) {
-			int ret = tag_get(*slot, tag, offset);
+			int ret = tag_get(slot, tag, offset);
 
 			BUG_ON(ret && saw_unset_tag);
 			return ret;
 		}
-		slot = (struct radix_tree_node **)((*slot)->slots + offset);
+		slot = slot->slots[offset];
 		shift -= RADIX_TREE_MAP_SHIFT;
 		height--;
 	}
@@ -472,17 +475,21 @@ __lookup(struct radix_tree_root *root, void **results, unsigned long index,
 	unsigned int max_items, unsigned long *next_index)
 {
 	unsigned int nr_found = 0;
-	unsigned int shift;
-	unsigned int height = root->height;
+	unsigned int shift, height;
 	struct radix_tree_node *slot;
+	unsigned long i;
+
+	height = root->height;
+	if (height == 0)
+		goto out;
 
 	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
 	slot = root->rnode;
 
-	while (height > 0) {
-		unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK;
+	for ( ; height > 1; height--) {
 
-		for ( ; i < RADIX_TREE_MAP_SIZE; i++) {
+		for (i = (index >> shift) & RADIX_TREE_MAP_MASK ;
+				i < RADIX_TREE_MAP_SIZE; i++) {
 			if (slot->slots[i] != NULL)
 				break;
 			index &= ~((1UL << shift) - 1);
@@ -492,22 +499,20 @@ __lookup(struct radix_tree_root *root, void **results, unsigned long index,
 		}
 		if (i == RADIX_TREE_MAP_SIZE)
 			goto out;
-		height--;
-		if (height == 0) {	/* Bottom level: grab some items */
-			unsigned long j = index & RADIX_TREE_MAP_MASK;
 
-			for ( ; j < RADIX_TREE_MAP_SIZE; j++) {
-				index++;
-				if (slot->slots[j]) {
-					results[nr_found++] = slot->slots[j];
-					if (nr_found == max_items)
-						goto out;
-				}
-			}
-		}
 		shift -= RADIX_TREE_MAP_SHIFT;
 		slot = slot->slots[i];
 	}
+
+	/* Bottom level: grab some items */
+	for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++) {
+		index++;
+		if (slot->slots[i]) {
+			results[nr_found++] = slot->slots[i];
+			if (nr_found == max_items)
+				goto out;
+		}
+	}
 out:
 	*next_index = index;
 	return nr_found;
@@ -655,6 +660,7 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
 {
 	struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;
 	struct radix_tree_path *orig_pathp;
+	struct radix_tree_node *slot;
 	unsigned int height, shift;
 	void *ret = NULL;
 	char tags[RADIX_TREE_TAGS];
@@ -666,25 +672,23 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
 
 	shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 	pathp->node = NULL;
-	pathp->slot = &root->rnode;
+	slot = root->rnode;
 
-	while (height > 0) {
+	for ( ; height > 0; height--) {
 		int offset;
 
-		if (*pathp->slot == NULL)
+		if (slot == NULL)
 			goto out;
 
 		offset = (index >> shift) & RADIX_TREE_MAP_MASK;
 		pathp[1].offset = offset;
-		pathp[1].node = *pathp[0].slot;
-		pathp[1].slot = (struct radix_tree_node **)
-				(pathp[1].node->slots + offset);
+		pathp[1].node = slot;
+		slot = slot->slots[offset];
 		pathp++;
 		shift -= RADIX_TREE_MAP_SHIFT;
-		height--;
 	}
 
-	ret = *pathp[0].slot;
+	ret = slot;
 	if (ret == NULL)
 		goto out;
 
@@ -704,10 +708,10 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
 			if (tags[tag])
 				continue;
 
-			tag_clear(pathp[0].node, tag, pathp[0].offset);
+			tag_clear(pathp->node, tag, pathp->offset);
 
 			for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
-				if (pathp[0].node->tags[tag][idx]) {
+				if (pathp->node->tags[tag][idx]) {
 					tags[tag] = 1;
 					nr_cleared_tags--;
 					break;
@@ -715,18 +719,19 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
 			}
 		}
 		pathp--;
-	} while (pathp[0].node && nr_cleared_tags);
+	} while (pathp->node && nr_cleared_tags);
 
-	pathp = orig_pathp;
-	*pathp[0].slot = NULL;
-	while (pathp[0].node && --pathp[0].node->count == 0) {
-		pathp--;
-		BUG_ON(*pathp[0].slot == NULL);
-		*pathp[0].slot = NULL;
-		radix_tree_node_free(pathp[1].node);
+	/* 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)
+			goto out;
+
+		/* Node with zero slots in use so free it */
+		radix_tree_node_free(pathp->node);
 	}
-	if (root->rnode == NULL)
-		root->height = 0;
+	root->rnode = NULL;
+	root->height = 0;
 out:
 	return ret;
 }