There is a significant energy improvement for PAVMr2 over PAVM, but this comes at a cost of page-migration overheads. Since we migrate pages only when the system is idle, avoiding interference with active processes, there is no direct performance overhead, and only an additional energy penalty is imposed for each page migrated. However, due to the periodic invocation of kmigrated and the check for system idle, there is an implicit limitation of migration to only the longer-lived processes. In Section 4.5, we have discussed other possible solutions to limit any overheads.
By logging page migration traffic, we determined that migration, with only the implicit limitation, accounts for only 2.7%, 0.8% and 0.8% of the total memory traffic for Light, Poweruser, and Multimedia workloads, respectively. If we adjust Figures 7(a-c) assuming maximal overhead reduction, we see no perceivable differences, so explicit attempts to reduce these overheads are not fruitful. Due to the significant energy savings and a fairly low overhead observed, page migration is beneficial in almost all circumstances.