Due to the unprecedented development of low-latency interconnect technology, building large-scale disaggregated architecture is drawing more and more attention from both industry and academia. Resource disaggregation is a new way to organize the hardware resources of datacenters, and has the potential to overcome the limitations, e.g., low resource utilization and low reliability, of conventional datacenters. However, the emerging disaggregated architecture brings severe performance and latency problems to the existing cloud systems. In this paper, we take memory disaggregation as an example to demonstrate the unique challenges that the disaggregated datacenter poses to the existing cloud software stacks, e.g., programming interface, language runtime, and operating system, and further discuss the possible ways to reinvent the cloud systems.