Page Faults

Suppose a process executes:

The CPU calculates the virtual address of status and attempts a write. The MMU cannot complete the access with the current translation state. Perhaps the virtual page has not yet been given a physical frame, the page is read-only, or the pointer does not belong to any valid region.

The processor cannot guess what the operating system intended. Instead, it stops the instruction's normal execution and transfers control to the kernel through a page fault.

A page fault is a synchronous processor exception raised when a virtual-memory access cannot complete using the current mappings and permissions.

The name sounds like an error, but many page faults are expected. The operating system can resolve some faults and retry the instruction without the application noticing. Other faults reveal an invalid access and are reported to the process.

Understanding this distinction turns “page fault” from a vague crash term into a precise operating-system event.

This chapter follows the hardware and kernel fault path, distinguishes recoverable from invalid accesses and minor from major faults, and shows how concurrency, scheduling, and residency affect fault behavior and latency.