F2FS_RESERVED_NODE_NUM
avail_user_node_count = sbi->total_node_count - F2FS_RESERVED_NODE_NUM;
F2FS_RESERVED_NODE_NUM;
avail_node_count = sbi->total_node_count - F2FS_RESERVED_NODE_NUM;
avail_node_count = sbi->total_node_count - F2FS_RESERVED_NODE_NUM;