Research On Architecture And Algorithm Of Live Migration In Xen Environment

System-level virtualization is becoming increasingly important because of their benefits in providing isolation,consolidation,containment and manageability.As one of the most important attributes of virtualization,live migration is able to completely and seamlessly migrate a virtual machine from one physical machine to another,which aims to provide efficient online system maintenance,reconfiguration,load balancing and proactive fault tolerance.It is desirable that VM migration be carried out in a very efficient manner,with both short migration time and low impact on hosted applications. The difficult of live migration now is how to cut down the total migration time and downtime.As an excellent open source virtual machine monitor under X86,Xen provides para-virtualization and hardware-assistant full virtualization.This paper focuses on the optimization of live migration in Xen environment,implementing a new architecture design,algorithm and experiments in order to reduce the migration time.The main contents of this paper are as follows:(1) According to the study of Xen architecture,key technology and sourc code,the paper analyses the factors that impact live migration.First,the default algorithm doesn't work well while dirty pages are frequent;second,the CPU scheduling is not appropriate during live migration.(2) Pre-copy module which contains layering-copy module and dirty-page decelerating module is designed to optimize framework for Xen live migration.. Pre-copy module mainly handles estimating the dirty-page rate before memory copy and decides when to use layering-copy module.(3) Based on the source codes of live migration in Xen,layering-copy algorithm and dirty-page decelerating algorithm are designed to improve the migration performance.Layering-copy algorithm can avoid the redundant copy of the same dirty page through counting the write times of memory page and separating them to three layers.Dirty-page decelerating algorithm can dynamicly adjust the CPU resources assigned to migrated domain.The cooperation of these two algorithms reduces the migration time while keeping the domain service.(4) Verify the rationality and feasibility of the two algorithms through experiments.The results show that layering-copy algorithm and dirty-page decelerating algorithm are efficient in high dirty-page rate environment.