Revisiting Swapping in User-space with Lightweight Threading
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Memory-intensive applications, such as in-memory databases, caching systems and key-value stores, are increasingly demanding larger main memory to fit their working sets. Conventional swapping can enlarge the memory capacity by paging out inactive pages to disks. However, the heavy I/O stack makes the traditional kernel-based swapping suffers from several critical performance issues. In this paper, we redesign the swapping system and propose LightSwap, an high-performance user-space swapping scheme that supports paging with both local SSDs and remote memories. First, to avoids kernel-involving, a novel page fault handling mechanism is proposed to handle page faults in user-space and further eliminates the heavy I/O stack with the help of user-space I/O drivers. Second, we co-design Lightswap with light weight thread (LWT) to improve system throughput and make it be transparent to user applications. Finally, we propose a try-catch framework in Lightswap to deal with paging errors which are exacerbated by the scaling in process technology. We implement Lightswap in our production-level system and evaluate it with YCSB workloads running on memcached. Results show that Ligthswap reduces the page faults handling latency by 3–5 times, and improves the throughput of memcached by more than 40
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