Key Techniques of Swapping Mechanism Based on Ultra-Low Latency SSD

With the rapid increase of memory-intensive applications, memory capacity is playing an increasingly prominent role in application requirements. However, particle density puts constraints on the DRAM memory capacity scalability. The swapping mechanism, known as a common memory-expansion technology, is to temporarily store less-used memory pages in devices to expand memory. In the past, the disk’s read/write speed was the main limit to prevent the wide adoption of the swapping mechanism. In recent years, with the rapid development of ultra-low latency SSDs, the swapping mechanism can take advantage of its low-latency read and write characteristics to improve the efficiency of swapping. The I/O stack of the swapping approach, however, has a significant software overhead with low I/O latency. We analyze and evaluate the Linux swapping mechanism using ultra-low latency SSDs and design Ultraswap, a swapping mechanism based on ultra-low latency SSDs. Ultraswap adds the processing of polling requests to the Linux I/O stack and reduces the I/O merging and scheduling overhead to achieve a lightweight I/O stack. Based on Ultraswap’s I/O stack, the swap-in and swap-out paths of the kernel swapping mechanism are further optimized. By optimizing the handling of faulted pages and direct memory recycling, the time overhead on the critical path of the swapping mechanism is reduced. The results show that Ultraswap can improve the average performance by 19% compared with Linux swapping mechanism; with 20% of local memory, Ultraswap can achieve a 33% performance improvement, effectively reducing the time overhead on the critical path of the swapping path.