lab2 init commit
merge lab1, fixed conflicts
Exercise1. modified boot_alloc()
Exercise 1. finished mem_init()
Exercise 1. finished page_alloc(), page_free()
Exercise 1 finished.
Exercise 4. finished pgdir_walk()
modified pgdir_walk()
boot_map_region()
lab2. Exercise4. page_lookup()
lab2. Exercise4. page_remove()
lab2. Exercise4. page_insert()
lab2. Exercise4. finished
lab2. Exercise 5. finished. lab2 finished
lab2 ok
lab3 init commit
git merge lab2
fixed some confilict bug
Lab3 PartA Exercise1 ok, add envs init
Lab3 PartA Exercise2 ok