Question

Discuss how frame sharing can be done using the Inverted Page Table when using a single Frame Table for logical-to-physical address mapping. (Slightly modify the diagram in Q.9a, if necessary, to support your answer.)

Q9.A: Discuss two advantages for sharing pages (or page frames).

Answer 1

1) As we all know that each operating system individually maintains an isolated page table for each which contains frames in it. When the process is very large and it is occupying the virtual memory then according to that size than the size of the page table which containing the frames also will be increased.

Inverted Page Table:

   It is one stack like structure. It has a one-page table for every frame present in the main memory. In the inverted page table, the number of entries of the pages is equal to the number of frames in the main memory. Here the thing is a single table is needed for mapping all the processes. It is mainly used to fight against the drawbacks of the page table. Each entry in the page table has a few fields in order to describe them. They are:

i) Page Number: It describes the range of the page number of the logical address.

ii) Process Id: Each and every inverted page table consists of address space information of all the processes which are under the execution. If two different processes have a similar virtual address then at that case the process id is used. Process Id acts as an address space identifier and gives a virtual page for a certain process which is mapped to that corresponding frame.

iii) Control Bits: Used to store extra-paging information which includes dirty bit, valid bit etc

iv) Chained Pointer: Two or more processes can share the one main memory. In this process, two or more logical pages mapped to one single page table.

Advantages of Sharing pages:

i) Sharing of pages can minimize the usage of RAM.

ii) Allocation of memory is very easy and also it is not much expensive.

iii) Swapping of pages is more efficient in the sharing of pages.

iv) Each process is allocated to one page separately then it consumes more memory in main memory if one process sharing the pages then it consumes less memory.