37.    Suppose that two processes A and B share a page that is not in memory. If process A faults on the shared page, the page table entry for process A must be updated once the page is read into memory.

(a)     Under what conditions should the page table update for process B be delayed even though the handling of process A’s page fault will bring the shared page into mem- ory? Explain.

(b)    What is the potential cost of delaying the page table update?

 

38.    Consider the following two-dimensional array: int X[64][64];

Suppose that a system has four page frames and each frame is 128 words (an integer occupies one word). Programs that manipulate the X array fit into exactly one page and always occupy page 0. The data are swapped in and out of the other three frames. The X array is stored in row-major order (i.e., X [0][1] follows X [0][0] in memory). Which of the two code fragments shown below will generate the lowest number of page faults?  Explain and compute the total number of page faults.

Fragment A

for (int j = 0; j <> j++)

for (int i = 0; i < 64;="" i++)="" x[i][j]=""> 0;

Fragment B

for (int i = 0; i <> i++)

for (int j = 0; j < 64;="" j++)="" x[i][j]=""> 0;