Enhancing LRU Replacement Via Phantom Associativity

In this paper, the authors propose a novel cache design, Phantom Associative Cache (PAC), that alleviates cache thrashing in L2 caches by keeping the in-cache data blocks for a longer time period. To realize PAC, they introduce the concept of phantom lines. A phantom line works like a real cache line in the LRU stack but does not hold any data or tag. When a phantom line is selected for replacement, cache bypassing is performed instead of replacement. By using appropriate number of phantom lines, PAC can always keep the data blocks that show stronger locality longer in the cache and bypass the cache for other blocks. They show that PAC can be implemented reasonably in practice.