問題文
A host is configured so that the sum of the memory assigned to its guests exceeds the physical memory installed. What makes that workable, and what is the risk?
選択肢
- Guests rarely use all of what they were assigned at the same time, and the host can reclaim unused pages; the risk is severe slowdown or failure if they do all demand it at once.
- The guests are given less memory than they asked for at boot, so the sum never actually exceeds the physical total, and an administrator adding up the assignments afterwards finds them matching the installed memory exactly.
- The host compresses the contents of memory so that the physical memory installed is effectively doubled, and the risk is that the compression itself consumes processor time which would otherwise have been available to the guests for the work they were created to perform.
- There is no risk, because the hypervisor refuses to start a guest that would exceed the physical total, which makes the sum of the assignments a ceiling that no administrator could cross by mistake.