Final answer:
When a page fault occurs before an executing instruction is complete, the instruction must be restarted.
Step-by-step explanation:
When a page fault occurs before an executing instruction is complete, the instruction must be restarted. This is because a page fault happens when a requested page is not in the main memory, and the operating system needs to bring it in from secondary storage. To do this, the instruction needs to be restarted from the beginning once the required page is available in memory.
Ignoring or completing the instruction would not be feasible in this scenario, as the required data is not available in memory, and the instruction cannot proceed until the page fault is resolved.