Page Fault

A page fault occurs when a process requests a page in memory but system can’t find it in memory. The system page fault handler attempts to resolve the page fault.

Type of Page Fault

• Hard Page Fault – If the requested Page retrieved from disk, the fault is called as hard page fault.

• Soft Page Fault - If the requested page found elsewhere in memory, the fault is called as soft page fault

*Most processors can handle large numbers of soft faults without significant consequence. However, hard faults can cause delays because they require disk access.

Given below counters can be used to identify the page faults.

Page Faults/sec - Page Faults/sec is a combination of hard page faults and soft page faults. This counter gives how many times page fault occurs. The Page must either be retrieved from another location in memory or from the pagefile.

Hard Page Fault Counter

·         Page Reads/sec – It indicates how often the system is reading the disk because of hard page faults. We can say, the number of pages reads from the disk that was done to satisfy page faults. The amount of pages read each time the system went to the disk may vary but a sustained value of over 5 is a strong indicator of a memory problem. We can say, counter is best indicator of a memory shortage.

·         Pages Input/sec - pages were read from disk to resolve hard page faults. We can use this counter in comparison with the Page Faults/sec counter to determine the percentage of the page faults that are hard page faults.

·         Pages/sec - pages were read from or written to disk to resolve hard page faults.

In short we can say, a high number of hard page faults may indicate that you need to increase the amount of memory or reduce the cache size on the server.

Soft Page Fault Counter

• Transition Faults/sec - page faults were resolved by recovering pages without additional disk activity, including pages that were being used by another process sharing the page.