LRU模拟：其基本原理为：如果某一个页面被访问了，它很可能还要被访问；相反，如果它长时间不被访问，再最近未来是不大可能被访问的。-LRU simulation: the basic principles: If a page was visited, which are likely to be visited　the other hand, if it is not a long visit, and then the future is unlikely to be a recent visit.