How to insert a delay in accessing swap space using Kernel Linux (6) source code?

I am looking for a way to insert some artificial delays when the operating system access the Swap Space. I am working on the latest version of kernel (Version 6.0.6 right now), I have found some locations in the kernel open source code that it handles page faults (do_page_fault()), but I am not sure if it is the right place to insert the delay?

I tried do_page_fault part in arch/x86/fault.c (I am using the ubuntu 22.04 for my testing). But no success. When making and updating kernel, sometimes it will insert so many delays and sometime it don’t.

>Solution :

There are two types of page faults: Major and Minor.

What you are looking for is recognized as Major Fault. There is a file called memory.c. in the function vm_fault_t do_swap_page(struct vm_fault *vmf) you can find the implementations of it, see the following code: (linux -> mm -> memory.c)

        if (!folio) {
            /*
             * Back out if somebody else faulted in this pte
             * while we released the pte lock.
             */
            vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
                    vmf->address, &vmf->ptl);
            if (likely(pte_same(*vmf->pte, vmf->orig_pte)))
                ret = VM_FAULT_OOM;
            goto unlock;
        }

        /* Had to read the page from swap area: Major fault */
        ret = VM_FAULT_MAJOR;
        count_vm_event(PGMAJFAULT);
        count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);