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Subject[PATCH 04/13] radixtree: look-aside cache
This introduces a set of lookup functions to radix tree for the read-ahead
logic. Other access patterns with high locality may also benefit from them.

Most of them are best inlined, so some macros/structs in .c are moved into .h.

- radix_tree_lookup_node(root, index, level)
Perform partial lookup, return the @level'th parent of the slot at
@index.

- radix_tree_cache_lookup(root, cache, index)
Perform lookup with the aid of a look-aside cache.
- radix_tree_cache_xxx()
Query various information about the cache.

- radix_tree_lookup_head(root, index, max_scan)
- radix_tree_lookup_tail(root, index, max_scan)
[head, tail) is a segment with continuous pages. The functions
search for the head and tail index of the segment at @index.

Signed-off-by: Wu Fengguang <wfg@mail.ustc.edu.cn>
---
include/linux/radix-tree.h | 149 ++++++++++++++++++++++++++++++++++++++++++++-
lib/radix-tree.c | 142 ++++++++++++++++++++++++++++++++----------
2 files changed, 254 insertions(+), 37 deletions(-)
--- linux-2.6.14-rc5-mm1.orig/include/linux/radix-tree.h
+++ linux-2.6.14-rc5-mm1/include/linux/radix-tree.h
@@ -22,12 +22,39 @@
#include <linux/preempt.h>
#include <linux/types.h>

+#ifdef __KERNEL__
+#define RADIX_TREE_MAP_SHIFT 6
+#else
+#define RADIX_TREE_MAP_SHIFT 3 /* For more stressful testing */
+#endif
+#define RADIX_TREE_TAGS 2
+
+#define RADIX_TREE_MAP_SIZE (1UL << RADIX_TREE_MAP_SHIFT)
+#define RADIX_TREE_MAP_MASK (RADIX_TREE_MAP_SIZE-1)
+
+#define RADIX_TREE_TAG_LONGS \
+ ((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)
+
+struct radix_tree_node {
+ unsigned int count;
+ void *slots[RADIX_TREE_MAP_SIZE];
+ unsigned long tags[RADIX_TREE_TAGS][RADIX_TREE_TAG_LONGS];
+};
+
struct radix_tree_root {
unsigned int height;
unsigned int gfp_mask;
struct radix_tree_node *rnode;
};

+/*
+ * Support access patterns with strong locality.
+ */
+struct radix_tree_cache {
+ unsigned long first_index;
+ struct radix_tree_node *tree_node;
+};
+
#define RADIX_TREE_INIT(mask) { \
.height = 0, \
.gfp_mask = (mask), \
@@ -45,9 +72,13 @@ do { \
} while (0)

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);
+void *radix_tree_lookup_node(struct radix_tree_root *, unsigned long,
+ unsigned int);
void *radix_tree_delete(struct radix_tree_root *, unsigned long);
+unsigned long radix_tree_lookup_head(struct radix_tree_root *root,
+ unsigned long index, unsigned int max_scan);
+unsigned long radix_tree_lookup_tail(struct radix_tree_root *root,
+ unsigned long index, unsigned int max_scan);
unsigned int
radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
unsigned long first_index, unsigned int max_items);
@@ -69,4 +100,118 @@ static inline void radix_tree_preload_en
preempt_enable();
}

+/**
+ * radix_tree_lookup - perform lookup operation on a radix tree
+ * @root: radix tree root
+ * @index: index key
+ *
+ * Lookup the item at the position @index in the radix tree @root.
+ */
+static inline void *radix_tree_lookup(struct radix_tree_root *root,
+ unsigned long index)
+{
+ return radix_tree_lookup_node(root, index, 0);
+}
+
+/**
+ * radix_tree_lookup_slot - lookup a slot in a radix tree
+ * @root: radix tree root
+ * @index: index key
+ *
+ * Lookup the slot corresponding to the position @index in the radix tree
+ * @root. This is useful for update-if-exists operations.
+ */
+static inline void **radix_tree_lookup_slot(struct radix_tree_root *root,
+ unsigned long index)
+{
+ struct radix_tree_node *node;
+
+ node = radix_tree_lookup_node(root, index, 1);
+ return node->slots + (index & RADIX_TREE_MAP_MASK);
+}
+
+/**
+ * radix_tree_cache_lookup_node - cached lookup node
+ * @root: radix tree root
+ * @cache: look-aside cache
+ * @index: index key
+ *
+ * Lookup the item at the position @index in the radix tree @root,
+ * and return the node @level levels from the bottom in the search path.
+ * @cache stores the last accessed upper level tree node by this
+ * function, and is always checked first before searching in the tree.
+ * It can improve speed for access patterns with strong locality.
+ * NOTE:
+ * - The cache becomes invalid on leaving the lock;
+ * - Do not intermix calls with different @level.
+ */
+static inline void *radix_tree_cache_lookup_node(struct radix_tree_root *root,
+ struct radix_tree_cache *cache,
+ unsigned long index, unsigned int level)
+{
+ struct radix_tree_node *node;
+ unsigned long i;
+ unsigned long mask;
+
+ if (level && level >= root->height)
+ return root->rnode;
+
+ i = ((index >> (level * RADIX_TREE_MAP_SHIFT)) & RADIX_TREE_MAP_MASK);
+ mask = ~((RADIX_TREE_MAP_SIZE << (level * RADIX_TREE_MAP_SHIFT)) - 1);
+
+ if ((index & mask) == cache->first_index)
+ return cache->tree_node->slots[i];
+
+ node = radix_tree_lookup_node(root, index, level + 1);
+ if (!node)
+ return 0;
+
+ cache->tree_node = node;
+ cache->first_index = (index & mask);
+ return node->slots[i];
+}
+
+/**
+ * radix_tree_cache_lookup - cached lookup page
+ * @root: radix tree root
+ * @cache: look-aside cache
+ * @index: index key
+ *
+ * Lookup the item at the position @index in the radix tree @root.
+ */
+static inline void *radix_tree_cache_lookup(struct radix_tree_root *root,
+ struct radix_tree_cache *cache,
+ unsigned long index)
+{
+ return radix_tree_cache_lookup_node(root, cache, index, 0);
+}
+
+static inline void radix_tree_cache_init(struct radix_tree_cache *cache)
+{
+ cache->first_index = 0x77;
+}
+
+static inline int radix_tree_cache_size(struct radix_tree_cache *cache)
+{
+ return RADIX_TREE_MAP_SIZE;
+}
+
+static inline int radix_tree_cache_count(struct radix_tree_cache *cache)
+{
+ if (cache->first_index != 0x77)
+ return cache->tree_node->count;
+ else
+ return 0;
+}
+
+static inline int radix_tree_cache_full(struct radix_tree_cache *cache)
+{
+ return radix_tree_cache_count(cache) == radix_tree_cache_size(cache);
+}
+
+static inline int radix_tree_cache_first_index(struct radix_tree_cache *cache)
+{
+ return cache->first_index;
+}
+
#endif /* _LINUX_RADIX_TREE_H */
--- linux-2.6.14-rc5-mm1.orig/lib/radix-tree.c
+++ linux-2.6.14-rc5-mm1/lib/radix-tree.c
@@ -32,25 +32,6 @@
#include <linux/bitops.h>


-#ifdef __KERNEL__
-#define RADIX_TREE_MAP_SHIFT 6
-#else
-#define RADIX_TREE_MAP_SHIFT 3 /* For more stressful testing */
-#endif
-#define RADIX_TREE_TAGS 2
-
-#define RADIX_TREE_MAP_SIZE (1UL << RADIX_TREE_MAP_SHIFT)
-#define RADIX_TREE_MAP_MASK (RADIX_TREE_MAP_SIZE-1)
-
-#define RADIX_TREE_TAG_LONGS \
- ((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)
-
-struct radix_tree_node {
- unsigned int count;
- void *slots[RADIX_TREE_MAP_SIZE];
- unsigned long tags[RADIX_TREE_TAGS][RADIX_TREE_TAG_LONGS];
-};
-
struct radix_tree_path {
struct radix_tree_node *node;
int offset;
@@ -282,8 +263,21 @@ int radix_tree_insert(struct radix_tree_
}
EXPORT_SYMBOL(radix_tree_insert);

-static inline void **__lookup_slot(struct radix_tree_root *root,
- unsigned long index)
+/**
+ * radix_tree_lookup_node - low level lookup routine
+ * @root: radix tree root
+ * @index: index key
+ * @level: stop at that many levels from bottom
+ *
+ * Lookup the item at the position @index in the radix tree @root.
+ * The return value is:
+ * @level == 0: page at @index;
+ * @level == 1: the corresponding bottom level tree node;
+ * @level < height: (height - @level)th level tree node;
+ * @level >= height: root node.
+ */
+void *radix_tree_lookup_node(struct radix_tree_root *root,
+ unsigned long index, unsigned int level)
{
unsigned int height, shift;
struct radix_tree_node *slot;
@@ -295,7 +289,7 @@ static inline void **__lookup_slot(struc
shift = (height-1) * RADIX_TREE_MAP_SHIFT;
slot = root->rnode;

- while (height > 0) {
+ while (height > level) {
if (slot == NULL)
return NULL;

@@ -306,36 +300,114 @@ static inline void **__lookup_slot(struc

return slot;
}
+EXPORT_SYMBOL(radix_tree_lookup_node);

/**
- * radix_tree_lookup_slot - lookup a slot in a radix tree
+ * radix_tree_lookup_head - lookup the head index
* @root: radix tree root
* @index: index key
+ * @max_scan: max items to scan
*
- * Lookup the slot corresponding to the position @index in the radix tree
- * @root. This is useful for update-if-exists operations.
+ * Lookup head index of the segment which contains @index. A segment is
+ * a set of continuous pages in a file.
+ * CASE RETURN VALUE
+ * no page at @index (not head) = @index + 1
+ * found in the range @index - @max_scan < (head index) <= @index
+ * not found in range (unfinished head) <= @index - @max_scan
*/
-void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
+unsigned long radix_tree_lookup_head(struct radix_tree_root *root,
+ unsigned long index, unsigned int max_scan)
{
- return __lookup_slot(root, index);
+ struct radix_tree_cache cache;
+ struct radix_tree_node *node;
+ int i;
+ unsigned long origin;
+
+ origin = index;
+ if (unlikely(max_scan > index))
+ max_scan = index;
+ radix_tree_cache_init(&cache);
+
+next_node:
+ if (origin - index > max_scan)
+ goto out;
+
+ node = radix_tree_cache_lookup_node(root, &cache, index, 1);
+ if (!node)
+ goto out;
+
+ if (node->count == RADIX_TREE_MAP_SIZE) {
+ if (index < RADIX_TREE_MAP_SIZE) {
+ index = -1;
+ goto out;
+ }
+ index = (index - RADIX_TREE_MAP_SIZE) | RADIX_TREE_MAP_MASK;
+ goto next_node;
+ }
+
+ for (i = index & RADIX_TREE_MAP_MASK; i >= 0; i--, index--) {
+ if (!node->slots[i])
+ goto out;
+ }
+
+ goto next_node;
+
+out:
+ return index + 1;
}
-EXPORT_SYMBOL(radix_tree_lookup_slot);
+EXPORT_SYMBOL(radix_tree_lookup_head);

/**
- * radix_tree_lookup - perform lookup operation on a radix tree
+ * radix_tree_lookup_tail - lookup the tail index
* @root: radix tree root
* @index: index key
+ * @max_scan: max items to scan
*
- * Lookup the item at the position @index in the radix tree @root.
+ * Lookup tail(pass the end) index of the segment which contains @index.
+ * A segment is a set of continuous pages in a file.
+ * CASE RETURN VALUE
+ * found in the range @index <= (tail index) < @index + @max_scan
+ * not found in range @index + @max_scan <= (non tail)
*/
-void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
+unsigned long radix_tree_lookup_tail(struct radix_tree_root *root,
+ unsigned long index, unsigned int max_scan)
{
- void **slot;
+ struct radix_tree_cache cache;
+ struct radix_tree_node *node;
+ int i;
+ unsigned long origin;
+
+ origin = index;
+ if (unlikely(index + max_scan < index))
+ max_scan = LONG_MAX - index;
+ radix_tree_cache_init(&cache);
+
+next_node:
+ if (index - origin >= max_scan)
+ goto out;

- slot = __lookup_slot(root, index);
- return slot != NULL ? *slot : NULL;
+ node = radix_tree_cache_lookup_node(root, &cache, index, 1);
+ if (!node)
+ goto out;
+
+ if (node->count == RADIX_TREE_MAP_SIZE) {
+ index = (index | RADIX_TREE_MAP_MASK) + 1;
+ if (unlikely(!index))
+ goto out;
+ goto next_node;
+ }
+
+ for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++, index++) {
+ if (!node->slots[i])
+ goto out;
+ }
+
+ goto next_node;
+
+out:
+ return index;
}
-EXPORT_SYMBOL(radix_tree_lookup);
+EXPORT_SYMBOL(radix_tree_lookup_tail);

/**
* radix_tree_tag_set - set a tag on a radix tree node
--
-
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