Research And Implementation Of Memory Deduplication In The Linux Desktop Environment

Memory management is one of the most important parts of the operating system.KSM (Kernel Samepage Merging) in Linux kernel is a kind of memory savingtechnology developed after the emerging of virtual machine. KSM can dramaticallydecrease the memory usage of the hypervisor running several virtual machines.Actually, KSM can also be applied to normal applications. But in order to use theKSM, application must explicitly evoke a system call in source code level to tell KSMthe memory area where the KSM will scan. To normal users, modifying the sourcecode is impossible at most of the time.Base on the full grasp of the implementation of KSM, a new implementationnamed KSM+is created, which allows users to merge same-content pages on thespecified applications without modifying corresponding source code. Moreover, theoriginal KSM algorithm relies heavily on the specified area is rich in same-contentpages, while normal applications have much less same-content pages compared tovirtual machines. So, when KSM is applied to those applications, it is possible thatmemory usage will rise rather than decrease. To combat with this situation, KSM+employs a new algorithm to decrease the memory usage for running itself. Severalexperiments prove that the KSM+can be easily applied to specified applications andmemory usage can be reduced. And a case is designed to compare the effect between KSM and KSM+, which shows KSM+behaves better in deduplication when thesame-content pages’ density is very low. At last, in order to inspect the characteristicsof same-content pages from normal desktop applications, an ad-hoc kernel module isdeveloped to do the statistics which supplies significant data for the furtherdevelopment of KSM+.