通过非易失存储和检查点优化缓解日志开销

发布时间：2018-04-28 13:47

本文选题：文件系统 + 非易失存储　；参考：《计算机研究与发展》2015年06期

【摘要】：在文件系统进行用户数据和元数据的持久化过程中,如果出现异常掉电或系统崩溃,可能导致文件系统出现数据的不一致性问题.现有的Ext4文件系统通过写前日志(write-ahead logging,WAL)技术结合事务机制来保证持久化操作的一致性.写前日志技术将文件系统元数据写入磁盘2次,元数据的粒度小、数量大、重复度高,影响了程序的性能,也缩短了Flash存储介质的使用寿命.针对这一问题,提出了使用新型非易失存储(non-volatile memory,NVM)作为存放日志的独立外部设备,并通过存取指令(load/store)接口直接访问;同时使用倒序扫描(reverse scan)技术对检查点(checkpoint)流程进行优化,减少同一数据块的重复写操作.实验结果表明,使用NVM作为外部日志分区,对于写操作比重较大的程序,在HDD上带宽提升接近50%;在SSD上带宽提升达到23%;在checkpoint时使用倒序扫描之后,写入次数降低明显,带宽提升接近20%.
[Abstract]:In the process of file system persistence of user data and metadata, if there is abnormal power failure or system crash, it may lead to the problem of data inconsistency in the file system. The existing Ext4 file system combines the transaction mechanism with the write-ahead logging technique to ensure the consistency of the persistence operation. The file system metadata is written to disk twice by the pre-write log technology. The metadata is small in granularity, large in quantity and high in repetition, which affects the performance of the program and shortens the service life of the Flash storage medium. In order to solve this problem, a new non-volatile memory NVM is proposed as an independent external device for storing logs, which can be accessed directly through the load-store interface of access instructions, and the checkpoint flow is optimized by using reverse scan technique. Reduce the repeat write operation of the same data block. The experimental results show that using NVM as an external log partition, for programs with a large proportion of write operations, the bandwidth increase is close to 50 on HDD, the bandwidth increase on SSD reaches 23 percent, and the number of writes decreases obviously after the use of inverted order scanning in checkpoint. Bandwidth gain is close to 20.
【作者单位】：首都师范大学信息工程学院;计算机体系结构国家重点实验室(中国科学院计算技术研究所);高可靠嵌入式系统技术北京市工程研究中心(首都师范大学);
【基金】：国家自然科学基金项目(61472260,61402302) 北京市自然科学基金项目(4143060) 计算机体系结构国家重点实验室开放课题(CARCH201203) 北京市属高等学校人才强教项目-国外访学(067135300100) 北京市属高等学校创新团队建设与教师职业发展计划基金项目(IDHT20150507)
【分类号】：TP333

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