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>

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);