[PATCH] radix-tree: direct data

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>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 114 insertions, 83 deletions

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index dd83cca28001..9158a68140c9 100644
--- a/include/linux/radix-tree.h
+++ b/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);
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 7097bb239e40..35a2d93b3528 100644
--- a/lib/radix-tree.c
+++ b/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_tree_node *node, unsigned int tag,
         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 radix_tree_root *root, unsigned long index)
 {
         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 radix_tree_root *root, unsigned long index)
                 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 radix_tree_root *root, unsigned long index)
 
                 /* 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_root *root,
         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_root *root,
         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_root *root,
                 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(struct radix_tree_root *root,
         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_tree_root *root,
         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_tree_root *root,
                 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_tree_root *root,
                         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_tree_root *root,
                 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_root *root,
         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_root *root,
                         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, void **results, unsigned long index,
         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 *root, void **results, unsigned long index,
         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 *root, void **results, unsigned long index,
                 }
                 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_tree_root *root, void **results,
         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(struct radix_tree_root *root)
 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_tree_root *root, unsigned long index)
         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_tree_root *root, unsigned long index)
                 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_tree_root *root, unsigned long index)
 
                 /* 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);