Crystal Gazer

Emerging non-volatile memory (NVM) technologies offer greater capacity than DRAM. Unfortunately, production NVM exhibits high latency and low write endurance. Hybrid memory combines DRAM and NVM to deliver greater capacity, low latency, high endurance, and low energy consumption.Write-rationing garbage collection mitigates NVM wear-out by placing highly-written objects in DRAM and the rest in NVM. Existing write-rationing garbage collectors dynamically monitor object writes to place highly written objects in DRAM. Unfortunately, monitoring writes incurs a non-negligible performance overhead. This work proposes Crystal Gazer, profile-driven write-rationing garbage collection for hybrid memories. Allocation sites are statically profiled, and highly written objects are predicted based on previous program executions. Unlike prior work, this paper exposes a Pareto trade-off between DRAM usage and NVM lifetime. Experimental results on an emulation platform show that Crystal Gazer eliminates the performance overhead of dynamic monitoring, while reducing more NVM writes than state-of-the-art write-rationing garbage collectors.