add wsclock and background page analysis job implementations

config.h

@@ -1,2 +1,3 @@
 #define PHYSICAL_PAGE_AMOUNT 64
-#define PAGE_REPLACEMENT_ALGORITHM 1
+#define PAGE_REPLACEMENT_ALGORITHM 2
+#define WSCLOCK_TIME_WINDOW 15

inc/kernel.h

@@ -18,6 +18,7 @@ void RUNQ_add_process(size_t max_page_accesses, size_t total_pages_owned);
 struct PhysPage {
 	size_t ppn;
 	size_t busy_flag;
+	size_t last_accessed;
 	struct PhysPage *prev;
 	struct PhysPage *next;
 	struct PageTableEntry *pt;
@@ -27,4 +28,6 @@ struct PhysPage {
 
 void KERNEL_page_fault(struct PageTableEntry *pt, size_t page_no);
 
+void KERNEL_update_job(size_t page_amount);
+
 #endif

src/kernel.c

@@ -12,6 +12,8 @@ extern struct RunQ *runq;
 extern struct PhysPage *first_free_page;
 extern struct PhysPage *first_busy_page;
 
+extern size_t system_time;
+
 
 struct RunQ *
 RunQ(size_t max_procs)
@@ -110,7 +112,83 @@ KERNEL_page_fault(struct PageTableEntry *pt, size_t page_no)
 
 		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");
+
+		// first pass (no reference flag + out of time window)
+		for (size_t i = 0; i < PHYSICAL_PAGE_AMOUNT; i++) {
+			if (first_busy_page->pt[first_busy_page->pt_index].r) {
+				printf("[kernel:page_fault:wsclock] ppn %d: r = 1, time %d -> %d\n",
+						first_busy_page->ppn, first_busy_page->last_accessed, system_time);
+				first_busy_page->last_accessed = system_time;
+				first_busy_page->pt[first_busy_page->pt_index].r = 0;
+
+				first_busy_page = first_busy_page->next;
+			} else if ((system_time - first_busy_page->last_accessed) > WSCLOCK_TIME_WINDOW) {
+				printf("[kernel:page_fault:wsclock] ppn %d: r = 0, time_window = %d (> WSCLOCK_TIME_WINDOW), using it\n",
+						first_busy_page->ppn, system_time - first_busy_page->last_accessed);
+				first_busy_page->pt[first_busy_page->pt_index].p = 0;
+				first_busy_page->pt = pt;
+				first_busy_page->pt_index = page_no;
+				pt[page_no].p = 1;
+				pt[page_no].ppn = first_busy_page->ppn;
+
+				first_busy_page = first_busy_page->next;
+
+				goto page_replacement_resolved;
+			} else {
+				printf("[kernel:page_fault:wsclock] ppn %d: r = 0, time_window = %d (<= WSCLOCK_TIME_WINDOW), still active\n",
+						first_busy_page->ppn, system_time - first_busy_page->last_accessed);
+
+				first_busy_page = first_busy_page->next;
+			}
+		}
+
+		// fallback to random
+		printf("[kernel:page_fault:wsclock] Failed to find non-active page, randomly selecting ppn %d\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:wsclock] Auto-advanced the list of busy pages to ppn %d\n", first_busy_page->ppn);
+
+page_replacement_resolved:
 		#endif
 	}
 }
+
+void KERNEL_update_job(size_t page_amount)
+{
+	if (first_busy_page == NULL) {
+		printf("[kernel:update_job] No pages to update\n");
+		return;
+	}
+
+	struct PhysPage *starting_page = first_busy_page;
+
+	for (size_t i = 0; i < page_amount; i++) {
+		if (first_busy_page->pt[first_busy_page->pt_index].r) {
+			printf("[kernel:update_job] ppn %d updated time %d -> %d\n", first_busy_page->ppn, first_busy_page->last_accessed, system_time);
+			first_busy_page->pt[first_busy_page->pt_index].r = 0;
+			first_busy_page->last_accessed = system_time;
+		} else {
+			printf("[kernel:update_job] ppn %d is up-to-date (time = %d)\n", first_busy_page->ppn, first_busy_page->last_accessed);
+		}
+
+		first_busy_page = first_busy_page->next;
+
+		if (first_busy_page == starting_page) {
+			printf("[kernel:update_job] Looped around the busy page list, exiting after %d iterations\n", i);
+			break;
+		}
+	}
+}

src/main.c

@@ -28,7 +28,7 @@ main(void)
 	first_free_page->prev = first_free_page;
 	first_free_page->next = first_free_page;
 
-	for (int i = 1; i <= PHYSICAL_PAGE_AMOUNT; i++) {
+	for (int i = 1; i < PHYSICAL_PAGE_AMOUNT; i++) {
 		struct PhysPage *pp = malloc(sizeof(struct PhysPage));
 		pp->ppn = i;
 		pp->busy_flag = 0;
@@ -50,12 +50,13 @@ main(void)
 
 	runq = RunQ(10);
 
-	for (size_t i = 0; i < 5; i++) {
+	for (size_t i = 0; i < 10; i++) {
-		RUNQ_add_process(10000, 10 + randint(70));
+		RUNQ_add_process(10000, 10 + randint(90));
 	}
 
-	for (int i = 0; i < 20; i++) {
+	for (int i = 0; i < 100; i++) {
-		PROCESS_run_for(runq->current_proc, 20);
+		PROCESS_run_for(runq->current_proc, 50);
 		runq->current_proc = runq->current_proc->next;
+		KERNEL_update_job(8);
 	}
 }