[PATCH v2 10/10] btrfs: relocation: Refactor the useless nodes handling into its own function

[Qu Wenruo <wqu@suse.com>]

This patch will also add some comment for the cleanup up.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/relocation.c | 111 ++++++++++++++++++++++++++++--------------
 1 file changed, 75 insertions(+), 36 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index b42c3d088be4..93364eb07a61 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1098,6 +1098,79 @@ static int finish_upper_links(struct backref_cache *cache,
 	return 0;
 }
 
+/*
+ * For useless nodes, do two major clean ups:
+ * - Cleanup the children edges and nodes
+ *   If child node is also orphan (no parent) during cleanup, then the
+ *   child node will also be cleaned up.
+ *
+ * - Freeing up leaves (level 0), keeps nodes detached
+ *   For nodes, the node is still cached as "detached"
+ *
+ * Return false if @node is not in the @useless_nodes list.
+ * Return true if @node is in the @useless_nodes list.
+ */
+static bool handle_useless_nodes(struct reloc_control *rc,
+				 struct list_head *useless_nodes,
+				 struct backref_node *node)
+{
+	struct backref_cache *cache = &rc->backref_cache;
+	bool ret = false;
+
+	while (!list_empty(useless_nodes)) {
+		struct backref_node *cur;
+
+		cur = list_entry(useless_nodes->next, struct backref_node,
+				 list);
+		list_del_init(&cur->list);
+
+		/* Only tree root nodes can be added to @useless_nodes */
+		ASSERT(list_empty(&cur->upper));
+
+		if (cur == node)
+			ret = true;
+
+		/* The node is the lowest node */
+		if (cur->lowest) {
+			list_del_init(&cur->lower);
+			cur->lowest = 0;
+		}
+
+		/* Cleanup the lower edges */
+		while (!list_empty(&cur->lower)) {
+			struct backref_edge *edge;
+			struct backref_node *lower;
+
+			edge = list_entry(cur->lower.next,
+					  struct backref_edge, list[UPPER]);
+			list_del(&edge->list[UPPER]);
+			list_del(&edge->list[LOWER]);
+			lower = edge->node[LOWER];
+			free_backref_edge(cache, edge);
+
+			/* Child node is also orphan, queue for cleanup */
+			if (list_empty(&lower->upper))
+				list_add(&lower->list, useless_nodes);
+		}
+		/* Mark this block processed for relocation */
+		mark_block_processed(rc, cur);
+
+		/*
+		 * Backref nodes for tree leaves are deleted from the cache.
+		 * Backref nodes for upper level tree blocks are left in the
+		 * cache to avoid unnecessary backref lookup.
+		 */
+		if (cur->level > 0) {
+			list_add(&cur->list, &cache->detached);
+			cur->detached = 1;
+		} else {
+			rb_erase(&cur->rb_node, &cache->rb_root);
+			free_backref_node(cache, cur);
+		}
+	}
+	return ret;
+}
+
 /*
  * build backref tree for a given tree block. root of the backref tree
  * corresponds the tree block, leaves of the backref tree correspond
@@ -1188,42 +1261,8 @@ struct backref_node *build_backref_tree(struct reloc_control *rc,
 		goto out;
 	}
 
-	/*
-	 * process useless backref nodes. backref nodes for tree leaves
-	 * are deleted from the cache. backref nodes for upper level
-	 * tree blocks are left in the cache to avoid unnecessary backref
-	 * lookup.
-	 */
-	while (!list_empty(&useless)) {
-		upper = list_entry(useless.next, struct backref_node, list);
-		list_del_init(&upper->list);
-		ASSERT(list_empty(&upper->upper));
-		if (upper == node)
-			node = NULL;
-		if (upper->lowest) {
-			list_del_init(&upper->lower);
-			upper->lowest = 0;
-		}
-		while (!list_empty(&upper->lower)) {
-			edge = list_entry(upper->lower.next,
-					  struct backref_edge, list[UPPER]);
-			list_del(&edge->list[UPPER]);
-			list_del(&edge->list[LOWER]);
-			lower = edge->node[LOWER];
-			free_backref_edge(cache, edge);
-
-			if (list_empty(&lower->upper))
-				list_add(&lower->list, &useless);
-		}
-		mark_block_processed(rc, upper);
-		if (upper->level > 0) {
-			list_add(&upper->list, &cache->detached);
-			upper->detached = 1;
-		} else {
-			rb_erase(&upper->rb_node, &cache->rb_root);
-			free_backref_node(cache, upper);
-		}
-	}
+	if (handle_useless_nodes(rc, &useless, node))
+		node = NULL;
 out:
 	btrfs_backref_iter_free(iter);
 	btrfs_free_path(path);
-- 
2.25.1