With multilevel page tables, a process’s PTE can be initialized when the process is first loaded, or each PTE can be initialized the first time its corresponding page is referenced. Similarly, the entire multilevel page table structure can be maintained in main memory, or parts of it can be sent to secondary storage. What are the costs and benefits of each approach?
What will be an ideal response?
Because most processes do not use their entire virtual address space, initializing all of
a process’s PTEs when the process is first loaded can result in significant execution-time and
memory overhead. If the operating system does not initialize each PTE until a process
attempts to reference the corresponding page, then the processor will raise an exception each
time the process references a page for the first time. The overhead due to such exceptions is
small if the process does not use much of its address space, but it can be significantly larger
than allocating all of a process’s PTEs at once, if the process references a large portion of its
pages. In general, because processes tend to be small and exhibit locality, the system experiences
good performance without initializing all of a process’s PTEs when it is first loaded.
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