[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>

1 files changed, 23 insertions, 17 deletions

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 1403e2c8bb3e..336852f23592 100644
--- 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--) {