NVM cache replacement policy

[pbhandar2]

NVM cache replacement policy

[therealgymmy]

On access, an item is promoted to DRAM from NVM. The NVM copy stays in NVM. Eventually when an item is evicted from DRAM, we check whether or not it is "clean" (i.e. does it have a copy in NVM). If it's clean, we will not evict it to nvm cache again since it's already present. See architecture guide: https://cachelib.org/docs/Cache_Library_Architecture_Guide/hybrid_cache#item-allocation-and-eviction

how does it make a difference to select FIFO or LRU

Item in NvmCache still age out in some order. FIFO or LRU in Navy governs the how these items eventually are evicted out of NvmCache. A frequently accessed item will stay in NvmCache for longer with a LRU policy compared to FIFO.