Answer from cs61c-ei (Jing Chen 16669246) for Question 2
The idea behind multi-level paging is mainly driven by the fact that a page table can be enormous for any process. Since each process has its own page table, there’s not enough room to have all these page tables residing in memory.

A second level page table exists only for valid entries of super level page table. Thus, it’s easier if the SPN is to the left of the 2PN because it serves as a “valid” check.