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SubjectRe: [PATCH] make radix tree gang lookup faster by using a bitmap search
From
Date
On Sat, 2005-08-27 at 10:53 -0700, Andrew Morton wrote:
> a) fix radix_tree_gang_lookup() to use find_next_bit()
>
> b) remove radix_tree_node.count
>
> c) Add a new tag field which simply means "present"
>
> d) remove radix_tree_gang_lookup() and __lookup() altogether
>
> e) Implement radix_tree_gang_lookup() via radix_tree_gang_lookup_tag()

OK, here it is: the combined version which treats the present bits as a
private tag, combines __lookup and __lookup_tag and does a fast bitmap
search for both.

James

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -32,22 +32,29 @@


#ifdef __KERNEL__
+#if BITS_PER_LONG == 32
+#define RADIX_TREE_MAP_SHIFT 5
+#elif BITS_PER_LONG == 64
#define RADIX_TREE_MAP_SHIFT 6
#else
+#error BITS_PER_LONG neither 32 nor 64
+#endif
+#define RADIX_TREE_MAP_FULL (~0UL)
+#else
#define RADIX_TREE_MAP_SHIFT 3 /* For more stressful testing */
+#define RADIX_TREE_MAP_FULL ((1UL << (1UL << RADIX_TREE_MAP_SHIFT)) - 1UL)
#endif
-#define RADIX_TREE_TAGS 2
+#define RADIX_TREE_USER_TAGS 2
+#define RADIX_TREE_TAG_PRESENT (RADIX_TREE_USER_TAGS + 0)
+/* Set this to the last private tag plus one */
+#define RADIX_TREE_TAGS (RADIX_TREE_TAG_PRESENT + 1)

#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];
+ unsigned long tags[RADIX_TREE_TAGS];
};

struct radix_tree_path {
@@ -133,21 +140,22 @@ int radix_tree_preload(int gfp_mask)
out:
return ret;
}
+EXPORT_SYMBOL(radix_tree_preload);

static inline void tag_set(struct radix_tree_node *node, int tag, int offset)
{
- if (!test_bit(offset, &node->tags[tag][0]))
- __set_bit(offset, &node->tags[tag][0]);
+ if ((node->tags[tag] & (1UL << offset)) == 0)
+ node->tags[tag] |= (1UL << offset);
}

static inline void tag_clear(struct radix_tree_node *node, int tag, int offset)
{
- __clear_bit(offset, &node->tags[tag][0]);
+ node->tags[tag] &= ~(1UL << offset);
}

static inline int tag_get(struct radix_tree_node *node, int tag, int offset)
{
- return test_bit(offset, &node->tags[tag][0]);
+ return (node->tags[tag] & (1UL << offset)) ? 1 : 0;
}

/*
@@ -184,15 +192,9 @@ static int radix_tree_extend(struct radi
* into the newly-pushed top-level node(s)
*/
for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {
- int idx;
-
tags[tag] = 0;
- for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
- if (root->rnode->tags[tag][idx]) {
- tags[tag] = 1;
- break;
- }
- }
+ if (root->rnode->tags[tag])
+ tags[tag] = 1;
}

do {
@@ -208,7 +210,7 @@ static int radix_tree_extend(struct radi
tag_set(node, tag, 0);
}

- node->count = 1;
+ node->tags[RADIX_TREE_TAG_PRESENT] = 1;
root->rnode = node;
root->height++;
} while (height > root->height);
@@ -251,8 +253,11 @@ int radix_tree_insert(struct radix_tree_
if (!(tmp = radix_tree_node_alloc(root)))
return -ENOMEM;
*slot = tmp;
- if (node)
- node->count++;
+ if (node) {
+ BUG_ON(tag_get(node, RADIX_TREE_TAG_PRESENT,
+ offset));
+ tag_set(node, RADIX_TREE_TAG_PRESENT, offset);
+ }
}

/* Go a level down */
@@ -265,11 +270,11 @@ int radix_tree_insert(struct radix_tree_

if (*slot != NULL)
return -EEXIST;
- if (node) {
- node->count++;
- BUG_ON(tag_get(node, 0, offset));
- BUG_ON(tag_get(node, 1, offset));
- }
+ BUG_ON(!node);
+ BUG_ON(tag_get(node, RADIX_TREE_TAG_PRESENT, offset));
+ tag_set(node, RADIX_TREE_TAG_PRESENT, offset);
+ BUG_ON(tag_get(node, 0, offset));
+ BUG_ON(tag_get(node, 1, offset));

*slot = item;
return 0;
@@ -399,13 +404,10 @@ void *radix_tree_tag_clear(struct radix_
goto out;

do {
- int idx;
-
tag_clear(pathp[0].node, tag, pathp[0].offset);
- for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
- if (pathp[0].node->tags[tag][idx])
- goto out;
- }
+ if (pathp[0].node->tags[tag])
+ goto out;
+
pathp--;
} while (pathp[0].node);
out:
@@ -468,8 +470,8 @@ EXPORT_SYMBOL(radix_tree_tag_get);
#endif

static unsigned int
-__lookup(struct radix_tree_root *root, void **results, unsigned long index,
- unsigned int max_items, unsigned long *next_index)
+__lookup_tag(struct radix_tree_root *root, void **results, unsigned long index,
+ unsigned int max_items, unsigned long *next_index, int tag)
{
unsigned int nr_found = 0;
unsigned int shift;
@@ -480,30 +482,48 @@ __lookup(struct radix_tree_root *root, v
slot = root->rnode;

while (height > 0) {
- unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK;
+ unsigned long j = (index >> shift) & RADIX_TREE_MAP_MASK, i;
+ unsigned long occupied_mask = 0;

- for ( ; i < RADIX_TREE_MAP_SIZE; i++) {
- if (slot->slots[i] != NULL)
- break;
- index &= ~((1UL << shift) - 1);
- index += 1UL << shift;
- if (index == 0)
- goto out; /* 32-bit wraparound */
- }
- if (i == RADIX_TREE_MAP_SIZE)
+ /* mark all the slots up to but excluding the starting
+ * index occupied */
+ occupied_mask = (1UL << j) - 1;
+ /* Now or in the remaining occupations (inverted so
+ * we can use ffz to find the next occupied slot) */
+ occupied_mask |= ~slot->tags[tag];
+
+ /* If everything from this on up is empty, then there's
+ * nothing more in the tree */
+ if (occupied_mask == RADIX_TREE_MAP_FULL) {
+ index = 0;
goto out;
+ }
+
+ i = ffz(occupied_mask);
+ if (i != j) {
+ index &= ~((1UL << (shift + RADIX_TREE_MAP_SHIFT)) - 1);
+ index |= i << shift;
+ }
+
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;
+ while (i < RADIX_TREE_MAP_SIZE) {
+ unsigned long occupied_mask;
+ BUG_ON(!slot->slots[i]);
+ results[nr_found++] = slot->slots[i];
+ if (nr_found == max_items) {
+ index++;
+ goto out;
}
+ occupied_mask = (1UL << i) - 1 + (1UL << i);
+ occupied_mask |= ~slot->tags[tag];
+ if (occupied_mask == RADIX_TREE_MAP_FULL)
+ break;
+ j = i;
+ i = ffz(occupied_mask);
+ index += i-j;
}
+ goto out;
}
shift -= RADIX_TREE_MAP_SHIFT;
slot = slot->slots[i];
@@ -540,8 +560,9 @@ radix_tree_gang_lookup(struct radix_tree

if (cur_index > max_index)
break;
- nr_found = __lookup(root, results + ret, cur_index,
- max_items - ret, &next_index);
+ nr_found = __lookup_tag(root, results + ret, cur_index,
+ max_items - ret, &next_index,
+ RADIX_TREE_TAG_PRESENT);
ret += nr_found;
if (next_index == 0)
break;
@@ -551,59 +572,6 @@ radix_tree_gang_lookup(struct radix_tree
}
EXPORT_SYMBOL(radix_tree_gang_lookup);

-/*
- * FIXME: the two tag_get()s here should use find_next_bit() instead of
- * open-coding the search.
- */
-static unsigned int
-__lookup_tag(struct radix_tree_root *root, void **results, unsigned long index,
- unsigned int max_items, unsigned long *next_index, int tag)
-{
- unsigned int nr_found = 0;
- unsigned int shift;
- unsigned int height = root->height;
- struct radix_tree_node *slot;
-
- shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
- slot = root->rnode;
-
- while (height > 0) {
- unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK;
-
- for ( ; i < RADIX_TREE_MAP_SIZE; i++) {
- if (tag_get(slot, tag, i)) {
- BUG_ON(slot->slots[i] == NULL);
- break;
- }
- index &= ~((1UL << shift) - 1);
- index += 1UL << shift;
- if (index == 0)
- goto out; /* 32-bit wraparound */
- }
- 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 (tag_get(slot, tag, j)) {
- BUG_ON(slot->slots[j] == NULL);
- results[nr_found++] = slot->slots[j];
- if (nr_found == max_items)
- goto out;
- }
- }
- }
- shift -= RADIX_TREE_MAP_SHIFT;
- slot = slot->slots[i];
- }
-out:
- *next_index = index;
- return nr_found;
-}
-
/**
* radix_tree_gang_lookup_tag - perform multiple lookup on a radix tree
* based on a tag
@@ -657,7 +625,7 @@ void *radix_tree_delete(struct radix_tre
struct radix_tree_path *orig_pathp;
unsigned int height, shift;
void *ret = NULL;
- char tags[RADIX_TREE_TAGS];
+ char tags[RADIX_TREE_TAGS - 1];
int nr_cleared_tags;

height = root->height;
@@ -691,27 +659,25 @@ void *radix_tree_delete(struct radix_tre
orig_pathp = pathp;

/*
- * Clear all tags associated with the just-deleted item
+ * Clear all user tags associated with the just-deleted item
*/
memset(tags, 0, sizeof(tags));
do {
int tag;

- nr_cleared_tags = RADIX_TREE_TAGS;
- for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {
- int idx;
-
+ /* The private tag RADIX_TREE_TAG_PRESENT is used to
+ * free the slots below, so don't clear it */
+ nr_cleared_tags = RADIX_TREE_TAGS - 1;
+ for (tag = 0; tag < RADIX_TREE_TAGS - 1;
+ tag++) {
if (tags[tag])
continue;

tag_clear(pathp[0].node, tag, pathp[0].offset);

- for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
- if (pathp[0].node->tags[tag][idx]) {
- tags[tag] = 1;
- nr_cleared_tags--;
- break;
- }
+ if (pathp[0].node->tags[tag]) {
+ tags[tag] = 1;
+ nr_cleared_tags--;
}
}
pathp--;
@@ -719,7 +685,12 @@ void *radix_tree_delete(struct radix_tre

pathp = orig_pathp;
*pathp[0].slot = NULL;
- while (pathp[0].node && --pathp[0].node->count == 0) {
+ BUG_ON(pathp[0].node &&
+ !tag_get(pathp[0].node, RADIX_TREE_TAG_PRESENT,
+ pathp[0].offset));
+ while (pathp[0].node &&
+ (pathp[0].node->tags[RADIX_TREE_TAG_PRESENT] &=
+ ~(1UL << pathp[0].offset)) == 0) {
pathp--;
BUG_ON(*pathp[0].slot == NULL);
*pathp[0].slot = NULL;
@@ -739,14 +710,11 @@ EXPORT_SYMBOL(radix_tree_delete);
*/
int radix_tree_tagged(struct radix_tree_root *root, int tag)
{
- int idx;
-
if (!root->rnode)
return 0;
- for (idx = 0; idx < RADIX_TREE_TAG_LONGS; idx++) {
- if (root->rnode->tags[tag][idx])
- return 1;
- }
+ if (root->rnode->tags[tag])
+ return 1;
+
return 0;
}
EXPORT_SYMBOL(radix_tree_tagged);

-
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