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Subject[PATCH 12/15] radixtree: introduce radix_tree_lookup_leaf_node()
This will be used by the pagecache context based read-ahead/read-around
heuristic to quickly check one pagecache range:
- if there is any hole
- if there is any pages

Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
include/linux/radix-tree.h | 2 ++
lib/radix-tree.c | 27 ++++++++++++++++++++++-----
2 files changed, 24 insertions(+), 5 deletions(-)
--- linux.orig/lib/radix-tree.c 2010-02-24 10:44:23.000000000 +0800
+++ linux/lib/radix-tree.c 2010-02-24 10:44:49.000000000 +0800
@@ -359,7 +359,7 @@ EXPORT_SYMBOL(radix_tree_insert);
* is_slot == 0 : search for the node.
*/
static void *radix_tree_lookup_element(struct radix_tree_root *root,
- unsigned long index, int is_slot)
+ unsigned long index, int is_slot, int level)
{
unsigned int height, shift;
struct radix_tree_node *node, **slot;
@@ -369,7 +369,7 @@ static void *radix_tree_lookup_element(s
return NULL;

if (!radix_tree_is_indirect_ptr(node)) {
- if (index > 0)
+ if (index > 0 || level > 0)
return NULL;
return is_slot ? (void *)&root->rnode : node;
}
@@ -390,7 +390,7 @@ static void *radix_tree_lookup_element(s

shift -= RADIX_TREE_MAP_SHIFT;
height--;
- } while (height > 0);
+ } while (height > level);

return is_slot ? (void *)slot:node;
}
@@ -410,7 +410,7 @@ static void *radix_tree_lookup_element(s
*/
void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
{
- return (void **)radix_tree_lookup_element(root, index, 1);
+ return (void **)radix_tree_lookup_element(root, index, 1, 0);
}
EXPORT_SYMBOL(radix_tree_lookup_slot);

@@ -428,11 +428,28 @@ EXPORT_SYMBOL(radix_tree_lookup_slot);
*/
void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
{
- return radix_tree_lookup_element(root, index, 0);
+ return radix_tree_lookup_element(root, index, 0, 0);
}
EXPORT_SYMBOL(radix_tree_lookup);

/**
+ * radix_tree_lookup_leaf_node - lookup leaf node on a radix tree
+ * @root: radix tree root
+ * @index: index key
+ *
+ * Lookup the leaf node that covers @index in the radix tree @root.
+ * Return NULL if the node does not exist, or is the special root node.
+ *
+ * The typical usage is to check the value of node->count, which shall be
+ * performed inside rcu_read_lock to prevent the node from being freed.
+ */
+struct radix_tree_node *
+radix_tree_lookup_leaf_node(struct radix_tree_root *root, unsigned long index)
+{
+ return radix_tree_lookup_element(root, index, 0, 1);
+}
+
+/**
* radix_tree_tag_set - set a tag on a radix tree node
* @root: radix tree root
* @index: index key
--- linux.orig/include/linux/radix-tree.h 2010-02-24 10:44:23.000000000 +0800
+++ linux/include/linux/radix-tree.h 2010-02-24 10:44:49.000000000 +0800
@@ -158,6 +158,8 @@ static inline void radix_tree_replace_sl
int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
+struct radix_tree_node *
+radix_tree_lookup_leaf_node(struct radix_tree_root *root, unsigned long index);
void *radix_tree_delete(struct radix_tree_root *, unsigned long);
unsigned int
radix_tree_gang_lookup(struct radix_tree_root *root, void **results,



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