Stack Usage Analysis for Efficient Wear Leveling in Non-Volatile Main Memory Systems

Emerging non-volatile memory (NVM) technologies, such as Phase Change Memory (PCM), have been considered as a replacement for DRAM and storage due to their low power consumption, fast access speed, and low unit cost. Even so, some NVMs have a significantly lower write endurance and hence in-memory wear leveling is an important requirement for practical applicability. Since writes to the stack often target a small and dense memory region, generic, coarse-grained wear-leveling mechanisms (e.g. virtual memory page remapping) are not sufficient. An alternative solution is to relocate the stack memory regularly, which involves copying of the stack content. As the stack content changes in size during the execution of an application, the copy overhead can be significantly mitigated by performing the relocation when the stack size is small.In this paper, we investigate two approaches to determine points in time when the stack is small. First, we analyze the possibility to fit simple machine-learning models to the stack usage function. Precise predictions of this function enable the identification of the minimum stack size during execution. In our evaluation, the tested models provide accurate estimates of the future stack usage function for a subset of common applications.As a second approach, we analyze applications a priori and determine potential optimal points to perform relocation in the instruction stream. In detail, we deploy the application in an analysis environment, which determines a rating for each executed instruction. Based on this rating, we apply a genetic algorithm to identify the best points in the instruction stream to perform the stack relocation. This approach allows to save up to 85% of the write overhead for wear-leveling in our experiments.