update lab1-8 codes and docs. now version is 0.2

code/lab6/kern/mm/vmm.c

@@ -460,6 +460,15 @@ do_pgfault(struct mm_struct *mm, uint32_t error_code, uintptr_t addr) {
     *    page_insert ： build the map of phy addr of an Page with the linear addr la
     *    swap_map_swappable ： set the page swappable
     */
+    /*
+     * LAB5 CHALLENGE ( the implmentation Copy on Write)
+		There are 2 situlations when code comes here.
+		  1) *ptep & PTE_P == 1, it means one process try to write a readonly page. 
+		     If the vma includes this addr is writable, then we can set the page writable by rewrite the *ptep.
+		     This method could be used to implement the Copy on Write (COW) thchnology(a fast fork process method).
+		  2) *ptep & PTE_P == 0 & but *ptep!=0, it means this pte is a  swap entry.
+		     We should add the LAB3's results here.
+     */
         if(swap_init_ok) {
             struct Page *page=NULL;
                                     //(1）According to the mm AND addr, try to load the content of right disk page