Page-fault trap occurs when a process tries to access these pages that have not yet been called into memory. Follow these steps:

1) check the internal page table of the process, usually saved with PCB. To determine the validity of the reference

2) if it is illegal, the process terminates; Otherwise, call in:

3) find a free frame

4) schedule a disk operation to bring the required pages into the newly allocated frame

5) after the disk read operation is completed, modify the internal table and page table (valid or invalid bits?) , indicates that the page is already in memory

6) restart the instruction interrupted by the trap.