how is page fault triggered in linux kernel

Question

I understand linux kernel implements demand paging - the page is not allocated until it is first access. This is all handled in the page fault handler. But what I don't understand is how is the page fault triggered? More precisely, what triggers the call of the page fault handler? Is it from hardware?

Answer 1

The page fault is caused by the CPU (more specifically, the MMU) whenever the application tries to access a virtual memory address which isn't mapped to a physical address. The page fault handler (in the kernel) then checks whether the page is currently swapped to disk (swaps it back in) or has been reserved but not committed (commits it), then sends control back to the application to retry the memory access instruction. If the application doesn't have that virtual address allocated, on the other hand, then it sends the segfault instruction back to the kernel.

So it's most accurate to say that the hardware triggers the call.

Answer 2

I recommend you to read "Modern Operating System 2nd Edition", chapter 4 is about Memory Management, this is a very complex topic. You should read it carefully.

Answer 3

when mapping onwards into memory that does not exist at all.( virtual to physical memory ).In this case, the MMU will say there is no corresponding physical memory and inform operating system which is known as a "page fault". The operating system tells it is a less used virtual memory and pls check it in disc .Then the page that the MMU was trying to find will be reloaded in place table. The memory map will be updated accordingly, then control will be given back user application at the exact point the page fault occured and perform that instruction again, only this time the MMU will output the correct address to the memory system, and all will continue.

Since page fault triggered by MMU which is part of hardware is responsible for it.