Understanding the limiting factors of page migration in hybrid main memory

Combining DRAM and non-volatile memory (NVM) has been proposed to increase capacity and reliability, and to decrease energy consumption. Software-managed hybrid memory is a promising way to incorporate NVM in main memory due to its architectural simplicity. However, there are significant performance issues caused by interference in the memory system due to data migration between DRAM and NVM and a lack of effective migration policies. We propose new analysis and simulation techniques to understand the behavior of software-managed hybrid memory. These techniques allow us to characterize the overhead experienced by requests in the memory hierarchy and identify the factors that limit performance in software-managed hybrid memory. We show that queuing delays at the NVM banks and NVM bus are the main limiting factors.