Reducing Energy of DRAM/Flash Memory System by OS-Controlled Data Refresh

This paper presents a new approach to reduce energy consumption of DRAM/flash memory system by lowering the frequency of DRAM refreshes. The approach is based on two ideas: a DRAM based swap-cache that reduces the number of writes to the flash memory by keeping dirty pages as long as possible; and OS-controlled page allocation/aging policy that stops refreshing for banks, whose pages are clean and not accessed for a long time. Simulations show that the approach can reduce the DRAM refresh energy by 59-74% and the overall energy of DRAM/flash memory system by 8-24% without increase in the execution.