Page Fault Explanation

[Hollow-man]

Can any one make me understand the concept of page fault? On XP i'm running a program that the performance monitor says its needs about 100-200M RAM. This is the only thing I am running on the machine. Some times it page faults like mad,near about 700.

[Nigel_123]

A virtual memory interrupt that signals that the next instruction or item of data is not in physical memory and must be swapped back in from the disk. If the required page on disk cannot be found, then a page fault error occurs, which means that either the operating system or an application has corrupted the virtual memory. If such an error occurs, the user has to reload the application.

[Tillie]

I think there are shirt periods where free memory goes to zero in you system and there is thrashing with many 100's of of page faults. I think I would try and get a graph of time and page faults.

[Nebersek]

Only those parts of the program and data that are currently in active use need to be held in physical RAM. Other parts are then held in a swap file (as it’s called in Windows 95/98/ME: Win386.swp) or page file (in Windows NT versions including Windows 2000 and XP: pagefile.sys). When a program tries to access some address that is not currently in physical RAM, it generates an interrupt, called a Page Fault. This asks the system to retrieve the 4 KB page containing the address from the page file (or in the case of code possibly from the original program file). This — a valid page fault — normally happens quite invisibly. Sometimes, through program or hardware error, the page is not there either. The system then has an ‘Invalid Page Fault’ error. This will be a fatal error if detected in a program: if it is seen within the system itself (perhaps because a program sent it a bad request to do something), it may manifest itself as a ‘blue screen’ failure with a STOP code: consult the page on STOP Messages on this site.

If there is pressure on space in RAM, then parts of code and data that are not currently needed can be ‘paged out’ in order to make room — the page file can thus be seen as an overflow area to make the RAM behave as if it were larger than it is.