| With the development of the embedded systems, the embedded operating system is widely used. As a result, the fileystem plays a critical role in the whole system. JFFS2 is a log-structured filesystem which is based on the flash memory. As a purely log-structured system, JFFS2 adapts completely new storage scheme, which is designed to meet the requirement of the wear-leveling and garbage-collection.At present, JFFS2 is growing perfect and mature increasingly, but because of the restrictions imposed by the flash technology and the designing aim of the JFFS2, there are several drawbacks still. It was designed for relatively small flash chips and has serious problems when it is used on large flash devices. It takes too much time to mount the filesystem. During the process, in order to manage the filesystem effectively, the system has to build many data structures which are necessary and inevitable. Furthermore, the memory spend on these data structure is a huge amount, compared with the relatively small memory in the embedded system, and meanwhile, the time complexity is linear with n, which is the amount of the node.The improvement strategy is to trade the the space for the time, it stores all the significant memory structure on the flash during umount process and reads all these information from it directly. Therefore, it becomes simpler to build the data structure and the system. For the sake of this, the first erase block is saved for the index information, by which the system can find out all the information stored in the flash before. The first mount is same to the original process and the system will store the information during the umount if there is no accidents.From the second time, all the mount processes just read the necessay information from the flash and there is wear-leveling issue due to the erasing time lower than the average number.According to the datas from the Arm-Linux platform, it proves that the improvement strategy speeds the process of the mount in a certait extent. |
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