add random page replacement method

src/kernel.c

@@ -5,6 +5,7 @@
 #include "kernel.h"
 #include "process.h"
 
+#include "config.h"
 
 extern struct RunQ *runq;
 
@@ -87,5 +88,29 @@ KERNEL_page_fault(struct PageTableEntry *pt, size_t page_no)
 			this_page->prev->next = this_page;
 			this_page->next->prev = this_page;
 		}
+	} else {
+		printf("[kernel:page_fault] No free pages available, trying to swap...\n");
+
+		#if PAGE_REPLACEMENT_ALGORITHM == 1
+		printf("[kernel:page_fault:random] Selected physical page #%d for replacement\n", first_busy_page->ppn);
+
+		// clear presence 'bit' from old PTE
+		first_busy_page->pt[first_busy_page->pt_index].p = 0;
+
+		// update physical page data
+		first_busy_page->pt = pt;
+		first_busy_page->pt_index = page_no;
+
+		// update PTE data
+		pt[page_no].p = 1;
+		pt[page_no].ppn = first_busy_page->ppn;
+
+		// move hand to next physical page
+		first_busy_page = first_busy_page->next;
+
+		printf("[kernel:page_fault:random] Auto-advanced the list of busy pages to ppn %d\n", first_busy_page->ppn);
+		#elif PAGE_REPLACEMENT_ALGORITHM == 2
+		printf("[kernel:page_fault:wsclock] Not implemented\n");
+		#endif
 	}
 }