SWEL-COFAE : Wear Leveling and Adaptive Encoding Assisted Compression of Frequent Words in Non-Volatile Main Memories

Emerging Non-Volatile memories such as Phase Change Memory (PCM) and Resistive RAM are projected as potential replacements of the traditional DRAM-based main memories. However, limited write endurance and high write energy limit their chances of adoption as a mainstream main memory standard. Therefore, developing solutions that enhance the lifetime of these memories while offering a decent system performance has a great impact in building future large capacity and energy-efficient main memories. In this paper, we propose a word-level compression scheme called COMF to reduce bitflips in PCMs by removing the most repeated words from the cache blocks before writing into memory. COMF is augmented with an adaptive granularity-based encoding technique to form COFAE, which reduces the bitflips to a further extent. We also propose SWEL-COFAE, an intra-line stride-based wear leveling technique to improve lifetime by balancing the bitflip pressure within the cells of the memory lines. Experimental results show that the proposed technique improves lifetime by 101% and reduces bitflips and energy by 59% and 61% respectively over baseline.