Multilevel paging is a paging scheme where there exists a hierarchy of page tables
The need for Multilevel paging
- To avoid the overhead of bringing large size page table in to memory ,the multilevel paging will be implemented
- In the multilevel paging ,paging will be applied on the page tables and instead of bringing the entire page tables in to memory ,the pages of page table will be brought in to main memory
Two level page table diagram
p1 no. of bits required to represents the pages of page table (outer page table) or page no. of page table
p2 no. of bits required to represents the page sige of page table or word number of the page of page table or page offset of page table
Three level page table diagram:
Important Points :
- In the multilevel paging when the paging applied on the page table,the last page table which we get is called as First level page table.
- In the multilevel paging when the paging applied on the page table, the first level page table entry contains base address of second level page table, second level page table entry contains the base address of third level page table and so on. The final page table entry contains frame number of actual page
- In the multilevel paging when the paging applied on the page tables,then whatever may be the levels of paging all the page table (page of page tables )will be stored in the main memory.
- In the multilevel paging when the paging applied on the page table,then whatever may be the levels of paging all the page table entries contains the frame number
- If page size is not mentioned in the problem then generally page size will be same in all the places(levels)
Ques. A computer has a 32 bit virtual address space and 1024 Bytes pages.A page table entry is 4 bytes.A multilevel page table is used because each page must fit in a page.How many levels are required ?
given data page size=1024 bytes
virtual address =32 bit
page table entry size=4 bytes
Page table size=(LAS/page size)*page table entry size
PTS1=(232/1024)*4B=224 cannot fit in a sngle page
PTS2=(224/1024)*4B = 216 cannot fit in a single page
PTS3=(216/1024)*4B=28 can be fit in a single page
therefore 3 levels are required to fit in a single page