CODEWITHSUNDEEP
linux-kernel
PMH
PMH

Reputation: 143

Does an entry of page table represents a page or a linear address?

I reading the book Understanding the linux kernel, and the topic about address transition very confuses me. Book says each linear address has three fields: Directory, Table, and Offset. The Directory field relates to the Directory Table, and Table field relates to Page Table.

One thing it does not point out, or I may miss, is that whether each entry in the tables relates to a page, which is a group of linear addresses, or relates to an individual linear address.

Can someone help me?

Upvotes: 1

Views: 670

Answers (1)

grill
grill

Reputation: 1170

Ok, so there are (at least) two types of page tables: single-level, and multi-level.

Single-level page tables' entries map directly to virtual addresses.

Multi-level page tables' entries can map to two different places:

  1. They may map directly to virtual memory addresses (like single-level tables).

  2. They may map to secondary (or tertiary, etc, etc.) page tables

    Here's an example of a multi-level page table: enter image description here

Remember, each page table entry holds a virtual address. It is the responsibility of the operating system to translate virtual addresses to physical addresses (the benefits of which are outside of this particular topic).

Most paging systems also maintain a frame table that keeps track of used and unused frames. The frame table is traditionally a different data structure than the page table.

You can read more about paging tables here. You can read about page tables here.

Upvotes: 1

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