ECR: Eviction-cost-aware cache management policy for page-level flash-based SSDs

摘要

Cache management policy plays a key role in offering low latency access to flash-based SSDs. Most existing solutions including LRU and its successors only focus on improving the cache hit ratio, but rarely consider to reduce the waiting time of the eviction operation in the page-level mapping FTLs. As the workloads spreading across internal chips of modern flash-based SSDs are often highly imbalanced when workloads are write-intensive, the time cost of evicting a dirty page from cache varies in a wide range. In this paper, we propose a novel eviction-cost-aware cache management policy, called ECR, to minimize the eviction cost in write-dominant applications. ECR gives a higher probability to evict a page, which causes the shortest waiting time in the corresponding chip queue. To achieve this, we introduce a monitor module to keep track of states of all chip queues, and a multi-LRU list structure to accelerate the selection of a victim chip and a target page in cache to perform an eviction. Our experimental results show that ECR can significantly reduce the average response time by as much as 59.55% and 44.84% compared to LRU and GCaR-CFLRU, respectively, where GCaR-CFLRU is the combination of state-of-the-art algorithm GCaR and CFLRU.