Address Space Creation

Address Space Creation

There are not sufficient TLB entries to describe all the address space of every process. The IRIX kernel creates a page table for each process, containing one entry for each virtual memory page in the address space of that process. Whenever an executing program refers to an address for which there is no current TLB entry, the processor traps to the handler for the TLB miss exception. The exception handler loads one TLB entry from the appropriate page table entry of the current process, in order to describe the needed virtual address. Then it resumes execution with the failed instruction.

The kernel maintains a page table in kernel memory for each process, and a page table for the kernel virtual address space as well. In order to extend a virtual address space, the kernel takes the following two steps.

It allocates unused page table entries to describe the needed pages. This defines the virtual addresses the pages will have.
It allocates page frames in memory to contain the pages themselves, and puts their physical addresses in the page table entries.