radix-tree: introduce radix_tree_replace_clear_tags()

In addition to replacing the entry, we also clear all associated tags.
This is really a one-off special for page_cache_tree_delete() which had
far too much detailed knowledge about how the radix tree works.

For efficiency, factor node_tag_clear() out of radix_tree_tag_clear() It
can be used by radix_tree_delete_item() as well as
radix_tree_replace_clear_tags().

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jan Kara <jack@suse.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 56 insertions, 52 deletions

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index bad63105e37e..11c8e7cc3920 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -281,9 +281,12 @@ bool __radix_tree_delete_node(struct radix_tree_root *root,
                               struct radix_tree_node *node);
 void *radix_tree_delete_item(struct radix_tree_root *, unsigned long, void *);
 void *radix_tree_delete(struct radix_tree_root *, unsigned long);
-unsigned int
-radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
-                        unsigned long first_index, unsigned int max_items);
+struct radix_tree_node *radix_tree_replace_clear_tags(
+                                struct radix_tree_root *root,
+                                unsigned long index, void *entry);
+unsigned int radix_tree_gang_lookup(struct radix_tree_root *root,
+                        void **results, unsigned long first_index,
+                        unsigned int max_items);
 unsigned int radix_tree_gang_lookup_slot(struct radix_tree_root *root,
                         void ***results, unsigned long *indices,
                         unsigned long first_index, unsigned int max_items);
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 9d9b4b9af4b6..c7114d233b38 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -740,6 +740,26 @@ void *radix_tree_tag_set(struct radix_tree_root *root,
 }
 EXPORT_SYMBOL(radix_tree_tag_set);
 
+static void node_tag_clear(struct radix_tree_root *root,
+                                struct radix_tree_node *node,
+                                unsigned int tag, unsigned int offset)
+{
+        while (node) {
+                if (!tag_get(node, tag, offset))
+                        return;
+                tag_clear(node, tag, offset);
+                if (any_tag_set(node, tag))
+                        return;
+
+                offset = node->offset;
+                node = node->parent;
+        }
+
+        /* clear the root's tag bit */
+        if (root_tag_get(root, tag))
+                root_tag_clear(root, tag);
+}
+
 /**
  *      radix_tree_tag_clear - clear a tag on a radix tree node
  *      @root:          radix tree root
@@ -776,28 +796,9 @@ void *radix_tree_tag_clear(struct radix_tree_root *root,
                 offset = radix_tree_descend(parent, &node, offset);
         }
 
-        if (node == NULL)
-                goto out;
+        if (node)
+                node_tag_clear(root, parent, tag, offset);
 
-        index >>= shift;
-
-        while (parent) {
-                if (!tag_get(parent, tag, offset))
-                        goto out;
-                tag_clear(parent, tag, offset);
-                if (any_tag_set(parent, tag))
-                        goto out;
-
-                index >>= RADIX_TREE_MAP_SHIFT;
-                offset = index & RADIX_TREE_MAP_MASK;
-                parent = parent->parent;
-        }
-
-        /* clear the root's tag bit */
-        if (root_tag_get(root, tag))
-                root_tag_clear(root, tag);
-
-out:
         return node;
 }
 EXPORT_SYMBOL(radix_tree_tag_clear);
@@ -1525,14 +1526,9 @@ void *radix_tree_delete_item(struct radix_tree_root *root,
 
         offset = get_slot_offset(node, slot);
 
-        /*
-         * Clear all tags associated with the item to be deleted.
-         * This way of doing it would be inefficient, but seldom is any set.
-         */
-        for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
-                if (tag_get(node, tag, offset))
-                        radix_tree_tag_clear(root, index, tag);
-        }
+        /* Clear all tags associated with the item to be deleted.  */
+        for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+                node_tag_clear(root, node, tag, offset);
 
         delete_sibling_entries(node, node_to_entry(slot), offset);
         node->slots[offset] = NULL;
@@ -1559,6 +1555,28 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index)
 }
 EXPORT_SYMBOL(radix_tree_delete);
 
+struct radix_tree_node *radix_tree_replace_clear_tags(
+                        struct radix_tree_root *root,
+                        unsigned long index, void *entry)
+{
+        struct radix_tree_node *node;
+        void **slot;
+
+        __radix_tree_lookup(root, index, &node, &slot);
+
+        if (node) {
+                unsigned int tag, offset = get_slot_offset(node, slot);
+                for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+                        node_tag_clear(root, node, tag, offset);
+        } else {
+                /* Clear root node tags */
+                root->gfp_mask &= __GFP_BITS_MASK;
+        }
+
+        radix_tree_replace_slot(slot, entry);
+        return node;
+}
+
 /**
  *      radix_tree_tagged - test whether any items in the tree are tagged
  *      @root:          radix tree root
diff --git a/mm/filemap.c b/mm/filemap.c
index b418405903bc..9665b1d4f318 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -114,14 +114,11 @@ static void page_cache_tree_delete(struct address_space *mapping,
                                    struct page *page, void *shadow)
 {
         struct radix_tree_node *node;
-        unsigned long index;
-        unsigned int offset;
-        unsigned int tag;
-        void **slot;
 
         VM_BUG_ON(!PageLocked(page));
 
-        __radix_tree_lookup(&mapping->page_tree, page->index, &node, &slot);
+        node = radix_tree_replace_clear_tags(&mapping->page_tree, page->index,
+                                                                shadow);
 
         if (shadow) {
                 mapping->nrexceptional++;
@@ -135,23 +132,9 @@ static void page_cache_tree_delete(struct address_space *mapping,
         }
         mapping->nrpages--;
 
-        if (!node) {
-                /* Clear direct pointer tags in root node */
-                mapping->page_tree.gfp_mask &= __GFP_BITS_MASK;
-                radix_tree_replace_slot(slot, shadow);
+        if (!node)
                 return;
-        }
-
-        /* Clear tree tags for the removed page */
-        index = page->index;
-        offset = index & RADIX_TREE_MAP_MASK;
-        for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
-                if (test_bit(offset, node->tags[tag]))
-                        radix_tree_tag_clear(&mapping->page_tree, index, tag);
-        }
 
-        /* Delete page, swap shadow entry */
-        radix_tree_replace_slot(slot, shadow);
         workingset_node_pages_dec(node);
         if (shadow)
                 workingset_node_shadows_inc(node);