[PATCH] radix tree: early termination of tag clearing

Correctly determine the tags to be cleared in radix_tree_delete() so we
don't keep moving up the tree clearing tags that we don't need to.  For
example, if a tag is simply not set in the deleted item, nor anywhere up
the tree, radix_tree_delete() would attempt to clear it up the entire
height of the tree.

Also, tag_set() was made conditional so as not to dirty too many cachelines
high up in the radix tree.  Instead, put this logic into
radix_tree_tag_set().

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 1403e2c..336852f 100644 (file)
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -137,18 +137,17 @@ out:
 
 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]);
+       __set_bit(offset, node->tags[tag]);
 }
 
 static inline void tag_clear(struct radix_tree_node *node, int tag, int offset)
 {
-       __clear_bit(offset, &node->tags[tag][0]);
+       __clear_bit(offset, node->tags[tag]);
 }
 
 static inline int tag_get(struct radix_tree_node *node, int tag, int offset)
 {
-       return test_bit(offset, &node->tags[tag][0]);
+       return test_bit(offset, node->tags[tag]);
 }
 
 /*
@@ -375,7 +374,8 @@ void *radix_tree_tag_set(struct radix_tree_root *root,
                int offset;
 
                offset = (index >> shift) & RADIX_TREE_MAP_MASK;
-               tag_set(slot, tag, offset);
+               if (!tag_get(slot, tag, offset))
+                       tag_set(slot, tag, offset);
                slot = slot->slots[offset];
                BUG_ON(slot == NULL);
                shift -= RADIX_TREE_MAP_SHIFT;
@@ -435,6 +435,8 @@ void *radix_tree_tag_clear(struct radix_tree_root *root,
                goto out;
 
        do {
+               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;
@@ -695,6 +697,8 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
        void *ret = NULL;
        char tags[RADIX_TREE_TAGS];
        int nr_cleared_tags;
+       int tag;
+       int offset;
 
        height = root->height;
        if (index > radix_tree_maxindex(height))
@@ -705,16 +709,14 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
        slot = root->rnode;
 
        for ( ; height > 0; height--) {
-               int offset;
-
                if (slot == NULL)
                        goto out;
 
+               pathp++;
                offset = (index >> shift) & RADIX_TREE_MAP_MASK;
-               pathp[1].offset = offset;
-               pathp[1].node = slot;
+               pathp->offset = offset;
+               pathp->node = slot;
                slot = slot->slots[offset];
-               pathp++;
                shift -= RADIX_TREE_MAP_SHIFT;
        }
 
@@ -727,24 +729,28 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
        /*
         * Clear all tags associated with the just-deleted item
         */
-       memset(tags, 0, sizeof(tags));
-       do {
-               int tag;
+       nr_cleared_tags = 0;
+       for (tag = 0; tag < RADIX_TREE_TAGS; tag++) {
+               if (tag_get(pathp->node, tag, pathp->offset)) {
+                       tag_clear(pathp->node, tag, pathp->offset);
+                       tags[tag] = 0;
+                       nr_cleared_tags++;
+               } else
+                       tags[tag] = 1;
+       }
 
-               nr_cleared_tags = RADIX_TREE_TAGS;
+       for (pathp--; nr_cleared_tags && pathp->node; pathp--) {
                for (tag = 0; tag < RADIX_TREE_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--;
                        }
                }
-               pathp--;
-       } while (pathp->node && nr_cleared_tags);
+       }
 
        /* Now free the nodes we do not need anymore */
        for (pathp = orig_pathp; pathp->node; pathp--) {