RePRAM: Re-cycling PRAM faulty blocks for extended lifetime

As main memory systems begin to face the scaling challenges from DRAM technology, future computer systems need to adapt to the emerging memory technologies like Phase-Change Memory (PCM or PRAM). While these newer technologies offer advantages such as storage density, non-volatility, and low energy consumption, they are constrained by limited write endurance that becomes more pronounced with process variation. In this paper, we propose a novel PRAM-based main memory system, RePRAM (Recycling PRAM), which leverages a group of faulty pages and recycles them in a managed way to significantly extend the PRAM lifetime while minimizing the performance impact. In particular, we explore two different dimensions of dynamic redundancy levels and group sizes, and design low-cost hardware and software support for RePRAM. Our proposed scheme involves minimal hardware modifications (that have less than 1% on-chip and off-chip area overheads). Also, our schemes can improve the PRAM lifetime by up to 43× (times) over a chip with no error correction capabilities, and outperform prior schemes such as DRM and ECP at a small fraction of the hardware cost. The performance overhead resulting from our scheme is less than 7% on average across 21 applications from SPEC2006, Splash-2, and PARSEC benchmark suites.