Answer from cs61c-cb (minh uyen nguyen 16765774) for Question 1
After a TLB miss occurs, TLB uses a write-back strategy (copying some certain entries back at miss time rather than whenever they are written)that is very efficient, since we expect the TLB miss rate to be small.
The exception for TLB entry missing is much more frequent than L1 cache, the operating system loads the TLB from the page table without examining the entry and restarts the instruction when such an exception occurs.  If the entry is avlid, another exception occurs, and the operating system recognizes that a page fault has occurred.  This method makes the frequent case of a TLB miss FAST, at a slight performance penalty for the infrequent case of a page fault.