3 files changed, 94 insertions, 37 deletions

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index b7edf825145..9d4539c52e5 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -252,6 +252,7 @@ unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
 		unsigned long nr_to_tag,
 		unsigned int fromtag, unsigned int totag);
 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);
+unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item);
 
 static inline void radix_tree_preload_end(void)
 {
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 348eaefbed7..a2f9da59c19 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -1203,6 +1203,98 @@ radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
 }
 EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);
 
+#if defined(CONFIG_SHMEM) && defined(CONFIG_SWAP)
+#include <linux/sched.h> /* for cond_resched() */
+
+/*
+ * This linear search is at present only useful to shmem_unuse_inode().
+ */
+static unsigned long __locate(struct radix_tree_node *slot, void *item,
+			      unsigned long index, unsigned long *found_index)
+{
+	unsigned int shift, height;
+	unsigned long i;
+
+	height = slot->height;
+	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
+
+	for ( ; height > 1; height--) {
+		i = (index >> shift) & RADIX_TREE_MAP_MASK;
+		for (;;) {
+			if (slot->slots[i] != NULL)
+				break;
+			index &= ~((1UL << shift) - 1);
+			index += 1UL << shift;
+			if (index == 0)
+				goto out;	/* 32-bit wraparound */
+			i++;
+			if (i == RADIX_TREE_MAP_SIZE)
+				goto out;
+		}
+
+		shift -= RADIX_TREE_MAP_SHIFT;
+		slot = rcu_dereference_raw(slot->slots[i]);
+		if (slot == NULL)
+			goto out;
+	}
+
+	/* Bottom level: check items */
+	for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
+		if (slot->slots[i] == item) {
+			*found_index = index + i;
+			index = 0;
+			goto out;
+		}
+	}
+	index += RADIX_TREE_MAP_SIZE;
+out:
+	return index;
+}
+
+/**
+ *	radix_tree_locate_item - search through radix tree for item
+ *	@root:		radix tree root
+ *	@item:		item to be found
+ *
+ *	Returns index where item was found, or -1 if not found.
+ *	Caller must hold no lock (since this time-consuming function needs
+ *	to be preemptible), and must check afterwards if item is still there.
+ */
+unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
+{
+	struct radix_tree_node *node;
+	unsigned long max_index;
+	unsigned long cur_index = 0;
+	unsigned long found_index = -1;
+
+	do {
+		rcu_read_lock();
+		node = rcu_dereference_raw(root->rnode);
+		if (!radix_tree_is_indirect_ptr(node)) {
+			rcu_read_unlock();
+			if (node == item)
+				found_index = 0;
+			break;
+		}
+
+		node = indirect_to_ptr(node);
+		max_index = radix_tree_maxindex(node->height);
+		if (cur_index > max_index)
+			break;
+
+		cur_index = __locate(node, item, cur_index, &found_index);
+		rcu_read_unlock();
+		cond_resched();
+	} while (cur_index != 0 && cur_index <= max_index);
+
+	return found_index;
+}
+#else
+unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
+{
+	return -1;
+}
+#endif /* CONFIG_SHMEM && CONFIG_SWAP */
 
 /**
  *	radix_tree_shrink    -    shrink height of a radix tree to minimal
diff --git a/mm/shmem.c b/mm/shmem.c
index 3a5be0feb6a..1c702f6f124 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -357,42 +357,6 @@ export:
 }
 
 /*
- * Lockless lookup of swap entry in radix tree, avoiding refcount on pages.
- */
-static pgoff_t shmem_find_swap(struct address_space *mapping, void *radswap)
-{
-	void  **slots[PAGEVEC_SIZE];
-	pgoff_t indices[PAGEVEC_SIZE];
-	unsigned int nr_found;
-
-restart:
-	nr_found = 1;
-	indices[0] = -1;
-	while (nr_found) {
-		pgoff_t index = indices[nr_found - 1] + 1;
-		unsigned int i;
-
-		rcu_read_lock();
-		nr_found = radix_tree_gang_lookup_slot(&mapping->page_tree,
-					slots, indices, index, PAGEVEC_SIZE);
-		for (i = 0; i < nr_found; i++) {
-			void *item = radix_tree_deref_slot(slots[i]);
-			if (radix_tree_deref_retry(item)) {
-				rcu_read_unlock();
-				goto restart;
-			}
-			if (item == radswap) {
-				rcu_read_unlock();
-				return indices[i];
-			}
-		}
-		rcu_read_unlock();
-		cond_resched();
-	}
-	return -1;
-}
-
-/*
  * Remove swap entry from radix tree, free the swap and its page cache.
  */
 static int shmem_free_swap(struct address_space *mapping,
@@ -612,7 +576,7 @@ static int shmem_unuse_inode(struct shmem_inode_info *info,
 	int error;
 
 	radswap = swp_to_radix_entry(swap);
-	index = shmem_find_swap(mapping, radswap);
+	index = radix_tree_locate_item(&mapping->page_tree, radswap);
 	if (index == -1)
 		return 0;