Laptop computers and tablet PCs currently exploit swap system with their second storage media as a cost effective solution to extend limited memory space. The rapidly evolving flash memory technology starts to replace the magnetic disks of these computers by flash memory due to its advantageous characteristics such as energy efficiency and mechanical shock resistance. Thus, we can imagine that the swap system running over flash memory will show up. However, since the contents of flash memory cannot be overwritten before being erased, we need a flash translation layer (FTL) to use flash memory as a disk transparently. Although FTLs help to deploy flash memory-based storage easily, the kernel and FTL sometimes make bad decisions because FTL cannot access kernel-level information and the kernel is not aware of flash memory states. In this paper, we mainly focus on the swap system running over flash memory. We discuss design and implementation of flash-aware swap system, called FASS, where the kernel manages flash memory-based swap space directly without FTL. This approach can utilize kernel information and flash memory states to optimize the system. On average, we show that our FASS reduces the number of flash read and write operations by 61 % and 41.5%.
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