Btrfs: unlock nodes earlier when inserting items in a btree

In ctree.c:setup_items_for_insert(), we can unlock all nodes in our
path before we process the leaf (shift items and data, adjust data
offsets, etc). This allows for better btree concurrency, as we're
often holding a write lock on at least the node at level 1.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/ctree.c

@@ -4738,6 +4738,12 @@ void setup_items_for_insert(struct btrfs_root *root, struct btrfs_path *path,
 	int slot;
 	struct btrfs_map_token token;
 
+	if (path->slots[0] == 0) {
+		btrfs_cpu_key_to_disk(&disk_key, cpu_key);
+		fixup_low_keys(root, path, &disk_key, 1);
+	}
+	btrfs_unlock_up_safe(path, 1);
+
 	btrfs_init_map_token(&token);
 
 	leaf = path->nodes[0];
@@ -4798,12 +4804,6 @@ void setup_items_for_insert(struct btrfs_root *root, struct btrfs_path *path,
 	}
 
 	btrfs_set_header_nritems(leaf, nritems + nr);
-
-	if (slot == 0) {
-		btrfs_cpu_key_to_disk(&disk_key, cpu_key);
-		fixup_low_keys(root, path, &disk_key, 1);
-	}
-	btrfs_unlock_up_safe(path, 1);
 	btrfs_mark_buffer_dirty(leaf);
 
 	if (btrfs_leaf_free_space(root, leaf) < 0) {