发表机构
Xiamen University; Shanghai Jiao Tong University（厦门大学; 上海交通大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
针对多级内存系统现有分层技术加剧层级竞争的问题，提出Mole系统，通过分离提升与降级目标、采用层级特定分析，减少迁移失败并提升动态访问下的性能。
AI 中文摘要
多级内存系统将快速、小型的上层内存与慢速、大型的下层内存相结合，以提升性能并优化成本效率。现有设计如AutoTiering和MTM依赖贪心提升与逐步降级策略，这会加剧快速层有限容量的竞争。我们观察到，提升操作直接改善性能，而降级操作主要用于回收空间，基于这种不对称性，我们提出Mole，一种分离提升与降级目标的内存分层系统。Mole采用暂存降级策略，将冷页直接移至最低层，绕过中间层；同时采用定向提升策略，将热页放置在与其当前热度匹配的层级。最低层作为暂存区，当页再次变热时可从该暂存区提升。这种分离策略可保留中间层容量用于提升操作，减少层级竞争与迁移失败。不过，暂存降级需要及时识别降级后变热的页，为以低分析开销满足此需求，Mole采用层级特定分析：高频分析最低层以检测重新激活的热页，低频分析上层以识别冷页。实验结果表明，Mole可减少迁移失败，并在动态访问模式下提升性能。
英文摘要
Multi-tiered memory systems combine fast, small upper tiers with slow, large lower tiers to improve performance and cost efficiency. Existing designs, such as AutoTiering and MTM, rely on greedy promotion and stepwise demotion, which can intensify contention for limited capacity in faster tiers. We observe that promotions directly improve performance, whereas demotions primarily reclaim space. Based on this asymmetry, we propose Mole, a memory tiering system that separates promotion and demotion destinations. Mole employs staging demotion to move cold pages directly to the lowest tier, bypassing intermediate tiers, and targeted promotion to place hot pages in tiers that match their current hotness. The lowest tier serves as a staging area from which pages can be promoted when they become hot again. This separation preserves intermediate-tier capacity for promotions, reducing tier contention and migration failures. However, staging demotion requires timely identification of pages that become hot after demotion. To meet this requirement with low profiling overhead, Mole uses tier-specific profiling: it profiles the lowest tier at high frequency to detect reactivated hot pages, while profiling upper tiers at lower frequency to identify cold pages. Experimental results show that Mole reduces migration failures and improves performance under dynamic access patterns.
