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What causes page faults?

Asked 2011-04-16T03:59:12.810
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According to Wikipedia:

A page fault is a trap to the software raised by the hardware when a program accesses a page that is mapped in the virtual address space, but not loaded in physical memory. (emphasis mine)

Okay, that makes sense.

But if that's the case, why is it that whenever the process information in Process Hacker is refreshed, I see about 15 page faults?

Screenshot

Or in other words, why is any memory getting paged out? (I have no idea if it's user or kernel memory.) I have no page file, and the RAM usage is about 1.2 GB out of 4 GB, which is after a clean reboot. There's no shortage of any resource; why would anything get paged out?

windows x86 paging x86-64
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2 Answers

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A slow but steady source of page faults is the OS probing for infrequently accessed pages. In this case, the operating system marks some pages not present, but leaves them in memory as-is. If an application accesses the page, then the #PF trap occurs and the OS simply marks the page present again without further ado. If a "long time" passes and a page never trips a fault, then the OS knows the page is a good candidate for swapping should the need arise. This mechanism can run proactively even in times of no resource pressure.

answered 2011-04-16T18:27:37.050
1

Operating Systems use paging to group items witch should be placed in physical memory and move them between physical memory and shared memory. most of the time, data items witch place in a single page, are related to each other. when data items in a page are not used for a long time, operating system moves it to virtual memory to free some space in physical memory. and then when a page is required witch is in virtual memory, operating system moves it from virtual memory (hard disk) to physical memory. this is Page Fault !

and remember, different operating systems are different in paging algorithms.

Basics of Page Faults

answered 2011-04-16T04:11:36.307

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