Clustered Page Tables
Clustered Page Tables and Hashed Page Tables are somehow similar to each other. But the main difference between these two tables is that Hashed Page Table refers to a single page whereas Cluster Page Table refers to mappings to multiple physical page frames in a single entry.
Clustered page Table is mostly used in sparse address spaces where non-contiguous address spaces are used for memory references.
Hashed Page Tables in Operating System
There are several common techniques for structuring page tables like Hierarchical Paging, Hashed Page Tables, and Inverted Page Tables. In this article, we will discuss the Hashed Page Table.
Hashed Page Tables are a type of data structure used by operating systems to efficiently manage memory mappings between virtual and physical memory addresses.
In Hashed Page Tables, the virtual page number in the virtual address is hashed into the hash table. They are used to handle address spaces higher than 32 bits. Each entry in the hash table has a linked list of elements hashing to the same location (to avoid collisions – as we can get the same value of a hash function for different page numbers). The hash value is the virtual page number. The Virtual Page Number is all the bits not part of the page offset.
For each element in the hash table, there are three fields
- Virtual Page Number (which is the hash value).
- Value of the mapped page frame.
- A pointer to the next element in the linked list.