Operating Systems Principle

Volume 3 Memory Management

1. In a single-threaded process, we can place the stack and heap at opposite ends of the virtual address space, and have them grow towards each other. However, with multiple threads preprocess, we need multiple thread stacks, each with room to grow.

Q：What is internal fragmentation ?

A: We can reduce the space taken up by the page table by choosing a larger page frame. How big should a page frame be ? A larger page frame can waste space if a process does not use all of the memory inside the frame. This is called internal fragmentation. Fixed-size chunks are easier to allocate, but waste space if the entire chunk is not used. Unfortunately, this means that with paging, either pages are very large (wasting space due to internal fragmentation), or the page table is very large ( wasting space), or both.

Q: What is translation look aside buffer (TLB) ?

A: A translation look aside buffer (TLB) is a small hardware table containing the results of recent address translations. Each entry in the TLB maps a virtual page to a physical page:

TLB 是MMU中包括了一个关于PTE的小的缓存，称为翻译后备缓冲器。