demand-paging.c

#include <unistd.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <err.h>

#define BUFFER_SIZE	(100 * 1024 * 1024)
#define NCYCLE		10
#define PAGE_SIZE	4096

int main(void)
{
	char *p;
	time_t t;
	char *s;

	t = time(NULL);
	s = ctime(&t);
	printf("%.*s: before allocation, please press Enter key\n",
	       (int)(strlen(s) - 1), s);
	getchar();

	p = malloc(BUFFER_SIZE);
	if (p == NULL)
		err(EXIT_FAILURE, "malloc() failed");

	t = time(NULL);
	s = ctime(&t);
	printf("%.*s: allocated %dMB, please press Enter key\n",
	       (int)(strlen(s) - 1), s, BUFFER_SIZE / (1024 * 1024));
	getchar();

	int i;
	for (i = 0; i < BUFFER_SIZE; i += PAGE_SIZE) {
		p[i] = 0;
		int cycle = i / (BUFFER_SIZE / NCYCLE);
		if (cycle != 0 && i % (BUFFER_SIZE / NCYCLE) == 0) {
			t = time(NULL);
			s = ctime(&t);
			printf("%.*s: touched %dMB\n",
			       (int) (strlen(s) - 1), s, i / (1024*1024));
			sleep(1);
		}
	}

	t = time(NULL);
	s = ctime(&t);
	printf("%.*s: touched %dMB, please press Enter key\n",
	       (int) (strlen(s) - 1), s, BUFFER_SIZE / (1024 * 1024));
	getchar();

	exit(EXIT_SUCCESS);
}