[PATCH 03/33] radixtree: hole scanning functions

Wu Fengguang
2006-05-24T11:28:38Z

[-- Attachment #1: radixtree-scan-hole.patch --]
[-- Type: text/plain, Size: 3784 bytes --]

Introduce a pair of functions to scan radix tree for hole/empty item.

include/linux/radix-tree.h | 4 +
lib/radix-tree.c | 104 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 108 insertions(+)

Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---

--- linux-2.6.17-rc4-mm3.orig/include/linux/radix-tree.h
+++ linux-2.6.17-rc4-mm3/include/linux/radix-tree.h
@@ -74,6 +74,10 @@ unsigned int radix_tree_cache_count(stru
void *radix_tree_cache_lookup_parent(struct radix_tree_root *root,
struct radix_tree_cache *cache,
unsigned long index, unsigned int level);
+unsigned long radix_tree_scan_hole_backward(struct radix_tree_root *root,
+ unsigned long index, unsigned long max_scan);
+unsigned long radix_tree_scan_hole(struct radix_tree_root *root,
+ unsigned long index, unsigned long max_scan);
unsigned int
radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
unsigned long first_index, unsigned int max_items);
--- linux-2.6.17-rc4-mm3.orig/lib/radix-tree.c
+++ linux-2.6.17-rc4-mm3/lib/radix-tree.c
@@ -427,6 +427,110 @@ unsigned int radix_tree_cache_count(stru
EXPORT_SYMBOL(radix_tree_cache_count);

/**
+ * radix_tree_scan_hole_backward - scan backward for hole
+ * @root: radix tree root
+ * @index: index key
+ * @max_scan: advice on max items to scan (it may scan a little more)
+ *
+ * Scan backward from @index for a hole/empty item, stop when
+ * - hit hole
+ * - @max_scan or more items scanned
+ * - hit index 0
+ *
+ * Return the correponding index.
+ */
+unsigned long radix_tree_scan_hole_backward(struct radix_tree_root *root,
+ unsigned long index, unsigned long max_scan)
+{
+ struct radix_tree_cache cache;
+ struct radix_tree_node *node;
+ unsigned long origin;
+ int i;
+
+ origin = index;
+ radix_tree_cache_init(&cache);
+
+ while (origin - index < max_scan) {
+ node = radix_tree_cache_lookup_parent(root, &cache, index, 1);
+ if (!node)
+ break;
+
+ if (node->count == RADIX_TREE_MAP_SIZE) {
+ index = (index - RADIX_TREE_MAP_SIZE) |
+ RADIX_TREE_MAP_MASK;
+ goto check_underflow;
+ }
+
+ for (i = index & RADIX_TREE_MAP_MASK; i >= 0; i--, index--) {
+ if (!node->slots[i])
+ goto out;
+ }
+
+check_underflow:
+ if (unlikely(index == ULONG_MAX)) {
+ index = 0;
+ break;
+ }
+ }
+
+out:
+ return index;
+}
+EXPORT_SYMBOL(radix_tree_scan_hole_backward);
+
+/**
+ * radix_tree_scan_hole - scan for hole
+ * @root: radix tree root
+ * @index: index key
+ * @max_scan: advice on max items to scan (it may scan a little more)
+ *
+ * Scan forward from @index for a hole/empty item, stop when
+ * - hit hole
+ * - hit EOF
+ * - hit index ULONG_MAX
+ * - @max_scan or more items scanned
+ *
+ * Return the correponding index.
+ */
+unsigned long radix_tree_scan_hole(struct radix_tree_root *root,
+ unsigned long index, unsigned long max_scan)
+{
+ struct radix_tree_cache cache;
+ struct radix_tree_node *node;
+ unsigned long origin;
+ int i;
+
+ origin = index;
+ radix_tree_cache_init(&cache);
+
+ while (index - origin < max_scan) {
+ node = radix_tree_cache_lookup_parent(root, &cache, index, 1);
+ if (!node)
+ break;
+
+ if (node->count == RADIX_TREE_MAP_SIZE) {
+ index = (index | RADIX_TREE_MAP_MASK) + 1;
+ goto check_overflow;
+ }
+
+ for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE;
+ i++, index++) {
+ if (!node->slots[i])
+ goto out;
+ }
+
+check_overflow:
+ if (unlikely(!index)) {
+ index = ULONG_MAX;
+ break;
+ }
+ }
+out:
+ return index;
+}
+EXPORT_SYMBOL(radix_tree_scan_hole);
+
+/**
* radix_tree_tag_set - set a tag on a radix tree node
* @root: radix tree root
* @index: index key

--