SRM-Buffer: An OS Buffer Management Technique to Prevent Last Level Caches from Thrashing in Multicores

Buffer caches in operating systems keep active file blocks in memory to reduce disk accesses. Related studies have focused on minimizing buffer misses and the resulting performance degradation. However, the side effects and performance implications of accessing the data in buffer caches (i.e. buffer cache hits) have been ignored. In this paper, we show that accessing buffer caches can cause serious performance degradation on multicores, particularly with shared last level caches (LLCs). There are two reasons for this problem. First, data objects in files normally have weaker localities than data objects in virtual memory spaces. Second, due to the shared structure of LLCs on multicore processors, an application accessing the data in a buffer cache may flush the to-be-reused data of its co-running applications from the shared LLC and significantly slow down these applications. The paper proposes a buffer cache design called Selected Region Mapping Buffer (SRM-buffer) for multicore systems to address effectively the cache pollution problem caused by OS buffer. SRM-buffer improves existing OS buffer management with an enhanced page allocation policy that carefully selects mapping physical pages upon buffer misses. For a sequence of blocks accessed by an application, SRMbuffer allocates physical pages that are mapped to a selected region consisting of a small portion of sets in the LLC. Thus, when these blocks are accessed, cache pollution is effectively limited within the small cache region. We have implemented a prototype of SRM-buffer into the Linux kernel, and tested it with extensive workloads. Performance evaluation shows SRM-buffer can improve system performance and decrease the execution times of workloads by up to 36%.