A page table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual addresses and physical addresses. It is somewhat slow to remove the page table entries of a process; the OS may avoid reusing per-process identifier values to delay facing this or it may elect to suffer the huge waste of memory associated with preallocated (necessary because of fragmentation) per-process hash tables. X86 Paging Structure. In the page table, each entry points to a physical address that is then mapped to the virtual address found by calculating the offset within the directory and the offset within the table. The topmost paging structure is the page directory. Once covered, it will be discussed how the lowest level entry, the Page Table Entry (PTE) and what bits are used by the hardware. Architectures implement these three lists in different ways but one method is through the use of a LIFO type structure.
Each running program, plus the data structures needed to manage it, is called a process. A page table is a data structure which consists of 220 page table entries (PTEs). On a typical x86 system, a page table entry requires 32 bits, so 1024 of them (covering 4MB of virtual address space) can be stored in one page. The Linux kernel works with a three-level structure which looks like this: On an x86 system running in the PAE mode (only needed when more than 4GB of memory is installed), all three levels of page tables are present. To do so, we need to keep a data structure (the page table) for each process mapping page numbers to frame numbers.
So how and where you (the operating system) wants to store the page tables and the page table entries is completely up to you. For example I did a project with a single inverted page table; I saw others using 2-level page tables per process. Multi-level tables are primarily needed because if the memory structure in Intel-land. Structure of the page table, Multilevel paging, Hashed page tables, Inverted page table, Protection under Paging, Hierarchical Paging, Address translation withinverted page table.
Please note that 4 bytes of a page table entry effectively stores multiple types of information apart from the base address of physical frame. If each entry is 32 bits, need 4M bytes of memory to store page table. On a TLB miss, search inverted page table data structure to find physical page frame for virtual address of process generating the access. Virtual memory address translation uses page tables. These are simple arrays in memory indexed by page number. Each page table entry contains information about a single page. The most important part of this information is a frame number where the page is located in physical memory. There is a mapping table, called the page table that exists in physcal memory. This is an enormous number of entries, especially considering that the virtual address space, by design, should be far larger than is ever required. It is also important to note that multi-level page tables consume more memory than single-level page tables if most of the address space is actually used; the difference is lost in the overhead of the additional structure. Set up a page table to translate logical to physical addresses. Valid-invalid bit attached to each entry in the page table: 1. Page Table Structure. 1.