Having Memory Storage Under Control of a File System

The development of memory storage device technologies, such as next generation non-volatile (NV) memory and battery backed NV-DIMM, has been advanced recently, and they became widely recognized. They provide high performance and persistency along with byte addressability. Their byte addressability enables CPUs to directly access them. Despite their clear advantages, their limited capacity makes it difficult to adapt them in the existing storage system, thus, their use cases have been limited. This paper proposes a method that for a file system to make use of memory storage as cache of block storage. Such use of memory storage makes it possible to access frequently accessed files efficiently since their data resides on memory storage and there is no need to access block storage. This method keeps memory storage under control of a file system. It enables the uses of the information that is available in the file system layer but is lost in the device driver layer. We implemented the proposed method in the file system layer of the Linux kernel. Its performance evaluation shows that it outperforms a bare SSD drive and a drive that combines memory storage and a SSD by the existing method.