[patch 1/3] radix-tree: direct data

Nick Piggin
2006-06-20T14:48:35Z

From: Nick Piggin <npiggin@suse.de>

The ability to have height 0 radix trees (a direct pointer to the data item
rather than going through a full node->slot) quietly disappeared with
old-2.6-bkcvs commit ffee171812d51652f9ba284302d9e5c5cc14bdfd. On 64-bit
machines this causes nearly 600 bytes to be used for every <= 4K file in
pagecache.

Re-introduce this feature, root tags stored in spare ->gfp_mask bits.

Simplify radix_tree_delete's complex tag clearing arrangement (which would
become even more complex) by just falling back to tag clearing functions
(the pagecache radix-tree never uses this path anyway, so the icache
savings will mean it's actually a speedup).

On my 4GB G5, this saves 8MB RAM per kernel kernel source+object tree in
pagecache.

Pagecache lookup, insertion, and removal speed for small files will also be
improved.

This makes RCU radix tree harder, but it's worth it.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Index: linux-2.6/include/linux/radix-tree.h
===================================================================
--- linux-2.6.orig/include/linux/radix-tree.h
+++ linux-2.6/include/linux/radix-tree.h
@@ -23,6 +23,9 @@
#include <linux/preempt.h>
#include <linux/types.h>

+#define RADIX_TREE_MAX_TAGS 2
+
+/* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
struct radix_tree_root {
unsigned int height;
gfp_t gfp_mask;
@@ -45,8 +48,6 @@ do { \
(root)->rnode = NULL; \
} while (0)

-#define RADIX_TREE_MAX_TAGS 2
-
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);
Index: linux-2.6/lib/radix-tree.c
===================================================================
--- linux-2.6.orig/lib/radix-tree.c
+++ linux-2.6/lib/radix-tree.c
@@ -74,6 +74,11 @@ struct radix_tree_preload {
};
DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };

+static inline gfp_t root_gfp_mask(struct radix_tree_root *root)
+{
+ return root->gfp_mask & __GFP_BITS_MASK;
+}
+
/*
* This assumes that the caller has performed appropriate preallocation, and
* that the caller has pinned this thread of control to the current CPU.
@@ -82,9 +87,10 @@ static struct radix_tree_node *
radix_tree_node_alloc(struct radix_tree_root *root)
{
struct radix_tree_node *ret;
+ gfp_t gfp_mask = root_gfp_mask(root);

- ret = kmem_cache_alloc(radix_tree_node_cachep, root->gfp_mask);
- if (ret == NULL && !(root->gfp_mask & __GFP_WAIT)) {
+ ret = kmem_cache_alloc(radix_tree_node_cachep, gfp_mask);
+ if (ret == NULL && !(gfp_mask & __GFP_WAIT)) {
struct radix_tree_preload *rtp;

rtp = &__get_cpu_var(radix_tree_preloads);
@@ -152,6 +158,27 @@ static inline int tag_get(struct radix_t
return test_bit(offset, node->tags[tag]);
}

+static inline void root_tag_set(struct radix_tree_root *root, unsigned int tag)
+{
+ root->gfp_mask |= (1 << (tag + __GFP_BITS_SHIFT));
+}
+
+
+static inline void root_tag_clear(struct radix_tree_root *root, unsigned int tag)
+{
+ root->gfp_mask &= ~(1 << (tag + __GFP_BITS_SHIFT));
+}
+
+static inline void root_tag_clear_all(struct radix_tree_root *root)
+{
+ root->gfp_mask &= __GFP_BITS_MASK;
+}
+
+static inline int root_tag_get(struct radix_tree_root *root, unsigned int tag)
+{
+ return root->gfp_mask & (1 << (tag + __GFP_BITS_SHIFT));
+}
+
/*
* Returns 1 if any slot in the node has this tag set.
* Otherwise returns 0.
@@ -182,7 +209,6 @@ static int radix_tree_extend(struct radi
{
struct radix_tree_node *node;
unsigned int height;
- char tags[RADIX_TREE_MAX_TAGS];
int tag;

/* Figure out what the height should be. */
@@ -195,16 +221,6 @@ static int radix_tree_extend(struct radi
goto out;
}

- /*
- * Prepare the tag status of the top-level node for propagation
- * into the newly-pushed top-level node(s)
- */
- for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
- tags[tag] = 0;
- if (any_tag_set(root->rnode, tag))
- tags[tag] = 1;
- }
-
do {
if (!(node = radix_tree_node_alloc(root)))
return -ENOMEM;
@@ -214,7 +230,7 @@ static int radix_tree_extend(struct radi

/* Propagate the aggregated tag info into the new root */
for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
- if (tags[tag])
+ if (root_tag_get(root, tag))
tag_set(node, tag, 0);
}

@@ -243,8 +259,7 @@ int radix_tree_insert(struct radix_tree_
int error;

/* Make sure the tree is high enough. */
- if ((!index && !root->rnode) ||
- index > radix_tree_maxindex(root->height)) {
+ if (index > radix_tree_maxindex(root->height)) {
error = radix_tree_extend(root, index);
if (error)
return error;
@@ -255,7 +270,7 @@ int radix_tree_insert(struct radix_tree_
shift = (height-1) * RADIX_TREE_MAP_SHIFT;

offset = 0; /* uninitialised var warning */
- do {
+ while (height > 0) {
if (slot == NULL) {
/* Have to add a child node. */
if (!(slot = radix_tree_node_alloc(root)))
@@ -273,16 +288,21 @@ int radix_tree_insert(struct radix_tree_
slot = node->slots[offset];
shift -= RADIX_TREE_MAP_SHIFT;
height--;
- } while (height > 0);
+ }

if (slot != NULL)
return -EEXIST;

- BUG_ON(!node);
- node->count++;
- node->slots[offset] = item;
- BUG_ON(tag_get(node, 0, offset));
- BUG_ON(tag_get(node, 1, offset));
+ 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;
+ BUG_ON(root_tag_get(root, 0));
+ BUG_ON(root_tag_get(root, 1));
+ }

return 0;
}
@@ -295,9 +315,13 @@ static inline void **__lookup_slot(struc
struct radix_tree_node **slot;

height = root->height;
+
if (index > radix_tree_maxindex(height))
return NULL;

+ if (height == 0 && root->rnode)
+ return (void **)&root->rnode;
+
shift = (height-1) * RADIX_TREE_MAP_SHIFT;
slot = &root->rnode;

@@ -368,8 +392,8 @@ void *radix_tree_tag_set(struct radix_tr
if (index > radix_tree_maxindex(height))
return NULL;

- shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
slot = root->rnode;
+ shift = (height - 1) * RADIX_TREE_MAP_SHIFT;

while (height > 0) {
int offset;
@@ -383,6 +407,10 @@ void *radix_tree_tag_set(struct radix_tr
height--;
}

+ /* set the root's tag bit */
+ if (slot && !root_tag_get(root, tag))
+ root_tag_set(root, tag);
+
return slot;
}
EXPORT_SYMBOL(radix_tree_tag_set);
@@ -405,9 +433,8 @@ void *radix_tree_tag_clear(struct radix_
unsigned long index, unsigned int tag)
{
struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path;
- struct radix_tree_node *slot;
+ struct radix_tree_node *slot = NULL;
unsigned int height, shift;
- void *ret = NULL;

height = root->height;
if (index > radix_tree_maxindex(height))
@@ -432,20 +459,24 @@ void *radix_tree_tag_clear(struct radix_
height--;
}

- ret = slot;
- if (ret == NULL)
+ if (slot == NULL)
goto out;

- do {
+ while (pathp->node) {
if (!tag_get(pathp->node, tag, pathp->offset))
goto out;
tag_clear(pathp->node, tag, pathp->offset);
if (any_tag_set(pathp->node, tag))
goto out;
pathp--;
- } while (pathp->node);
+ }
+
+ /* clear the root's tag bit */
+ if (root_tag_get(root, tag))
+ root_tag_clear(root, tag);
+
out:
- return ret;
+ return slot;
}
EXPORT_SYMBOL(radix_tree_tag_clear);

@@ -458,9 +489,8 @@ EXPORT_SYMBOL(radix_tree_tag_clear);
*
* Return values:
*
- * 0: tag not present
- * 1: tag present, set
- * -1: tag present, unset
+ * 0: tag not present or not set
+ * 1: tag set
*/
int radix_tree_tag_get(struct radix_tree_root *root,
unsigned long index, unsigned int tag)
@@ -473,6 +503,13 @@ int radix_tree_tag_get(struct radix_tree
if (index > radix_tree_maxindex(height))
return 0;

+ /* check the root's tag bit */
+ if (!root_tag_get(root, tag))
+ return 0;
+
+ if (height == 0)
+ return 1;
+
shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
slot = root->rnode;

@@ -494,7 +531,7 @@ int radix_tree_tag_get(struct radix_tree
int ret = tag_get(slot, tag, offset);

BUG_ON(ret && saw_unset_tag);
- return ret ? 1 : -1;
+ return ret;
}
slot = slot->slots[offset];
shift -= RADIX_TREE_MAP_SHIFT;
@@ -514,8 +551,11 @@ __lookup(struct radix_tree_root *root, v
unsigned long i;

height = root->height;
- if (height == 0)
+ if (height == 0) {
+ if (root->rnode && index == 0)
+ results[nr_found++] = root->rnode;
goto out;
+ }

shift = (height-1) * RADIX_TREE_MAP_SHIFT;
slot = root->rnode;
@@ -603,10 +643,16 @@ __lookup_tag(struct radix_tree_root *roo
unsigned int height = root->height;
struct radix_tree_node *slot;

+ if (height == 0) {
+ if (root->rnode && index == 0)
+ results[nr_found++] = root->rnode;
+ goto out;
+ }
+
shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
slot = root->rnode;

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

for ( ; i < RADIX_TREE_MAP_SIZE; i++) {
@@ -637,7 +683,7 @@ __lookup_tag(struct radix_tree_root *roo
}
shift -= RADIX_TREE_MAP_SHIFT;
slot = slot->slots[i];
- }
+ } while (height > 0);
out:
*next_index = index;
return nr_found;
@@ -665,6 +711,10 @@ radix_tree_gang_lookup_tag(struct radix_
unsigned long cur_index = first_index;
unsigned int ret = 0;

+ /* check the root's tag bit */
+ if (!root_tag_get(root, tag))
+ return 0;
+
while (ret < max_items) {
unsigned int nr_found;
unsigned long next_index; /* Index of next search */
@@ -689,7 +739,7 @@ EXPORT_SYMBOL(radix_tree_gang_lookup_tag
static inline void radix_tree_shrink(struct radix_tree_root *root)
{
/* try to shrink tree height */
- while (root->height > 1 &&
+ while (root->height > 0 &&
root->rnode->count == 1 &&
root->rnode->slots[0]) {
struct radix_tree_node *to_free = root->rnode;
@@ -717,12 +767,8 @@ static inline void radix_tree_shrink(str
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;
+ struct radix_tree_node *slot = NULL;
unsigned int height, shift;
- void *ret = NULL;
- char tags[RADIX_TREE_MAX_TAGS];
- int nr_cleared_tags;
int tag;
int offset;

@@ -730,11 +776,17 @@ void *radix_tree_delete(struct radix_tre
if (index > radix_tree_maxindex(height))
goto out;

+ slot = root->rnode;
+ if (height == 0 && root->rnode) {
+ root_tag_clear_all(root);
+ root->rnode = NULL;
+ goto out;
+ }
+
shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
pathp->node = NULL;
- slot = root->rnode;

- for ( ; height > 0; height--) {
+ do {
if (slot == NULL)
goto out;

@@ -744,44 +796,22 @@ void *radix_tree_delete(struct radix_tre
pathp->node = slot;
slot = slot->slots[offset];
shift -= RADIX_TREE_MAP_SHIFT;
- }
+ height--;
+ } while (height > 0);

- ret = slot;
- if (ret == NULL)
+ if (slot == NULL)
goto out;

- orig_pathp = pathp;
-
/*
* Clear all tags associated with the just-deleted item
*/
- nr_cleared_tags = 0;
for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
- tags[tag] = 1;
- if (tag_get(pathp->node, tag, pathp->offset)) {
- tag_clear(pathp->node, tag, pathp->offset);
- if (!any_tag_set(pathp->node, tag)) {
- tags[tag] = 0;
- nr_cleared_tags++;
- }
- }
- }
-
- for (pathp--; nr_cleared_tags && pathp->node; pathp--) {
- for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
- if (tags[tag])
- continue;
-
- tag_clear(pathp->node, tag, pathp->offset);
- if (any_tag_set(pathp->node, tag)) {
- tags[tag] = 1;
- nr_cleared_tags--;
- }
- }
+ if (tag_get(pathp->node, tag, pathp->offset))
+ radix_tree_tag_clear(root, index, tag);
}

/* Now free the nodes we do not need anymore */
- for (pathp = orig_pathp; pathp->node; pathp--) {
+ while (pathp->node) {
pathp->node->slots[pathp->offset] = NULL;
pathp->node->count--;

@@ -793,11 +823,15 @@ void *radix_tree_delete(struct radix_tre

/* Node with zero slots in use so free it */
radix_tree_node_free(pathp->node);
+
+ pathp--;
}
- root->rnode = NULL;
+ root_tag_clear_all(root);
root->height = 0;
+ root->rnode = NULL;
+
out:
- return ret;
+ return slot;
}
EXPORT_SYMBOL(radix_tree_delete);

@@ -808,11 +842,7 @@ EXPORT_SYMBOL(radix_tree_delete);
*/
int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag)
{
- struct radix_tree_node *rnode;
- rnode = root->rnode;
- if (!rnode)
- return 0;
- return any_tag_set(rnode, tag);
+ return root_tag_get(root, tag);
}
EXPORT_SYMBOL(radix_tree_tagged);