Flash-based Solid-state Disk Research For Memory Swap Technology

Memory swapping technology is applied to almost all computer systems, frequent accessto external storage in memory swap operations significantly decreases the performance ofapplications. In recent years, with the rapid development of flash which is considered as newstorage medium, more and more research focus on using flash solid-state disk as swap area,so as to effectively reduce I/O access latency in swap system, and improve performance ofapplications. Based on flash solid-state disk itself characteristics, this paper respectivelyexplore data deduplication and space allocation in swap area.In terms of data deduplication in memory swap area, the paper proposes a memory swapmechanism of combination with data deduplication MSDD (Memory Swap with DataDeduplication), by deleting repeated pages’ swapping out operations, and reduce flashsolid-state disk’s I/O write operations, to prolong the service life of flash solid-state disk.Given that the swapping out operation is sensitive to the operation latency and the size of theavailable memory, MSDD uses the improved MD5algorithm to efficiently calculate digitalfingerprints of pages and stores deduplication metadata by employing the hash-table tobalance the size of memory occupancy and the retrieval time of deduplication metadata.In terms of space allocation in memory swap area, the paper puts forward a kind of swaparea space allocation scheme with semantic perception. Using flash solid-state disk as swaparea, flash solid-state disk can’t perceive swap area’s invalid data, memory swap system needsto send the Trim command to inform flash memory solid-state disk of the invalid data’slocation, so that flash solid-state disk can recovery of invalid data page, but at the same timethe Trim command introduces a certain amount of time overhead for memory swap system.Based on flash solid-state disk’s semantic gap, space allocation proposed by the paper has thefunction of semantic transfer and reduces the times of Trim command, thereby reducing timeoverhead of memory swap system, further improving the performance of applications.Four kinds of typical applications’ experimental test results show that using flashsolid-state disk as swap area can effectively improve the performance of applications. Thispaper proposes MSDD mechanism from the perspective of memory swap area’s deletingredundant, to reduce flash solid-state disk’s write operations and extend the service life of theflash solid-state disk, and the time and space costs of MSDD mechanism are within theacceptable range; the paper proposes swap space allocation scheme of with semanticperception,the scheme saves the time overhead of swap area’s space allocation in memory swap system by merging the Trim command and minimize Trim command usage, furtherimprove the performance of applications.