#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <errno.h>
#include <stdio.h>
main(int argc,char *argv[])
{
	unsigned long siz, procs, itterations, cow;
	char	*ptr1;
	char	*i;
	int	pid, j, k, status;

	if ((argc <= 1)||(argc >4)) {
		printf("bad args, usage: forkoff <memsize-in-GB> #children #itterations cow:0|1\n");
		exit(-1);
	}
	siz = ((long)atol(argv[1])*1024*1024*1024);
	procs = atol(argv[2]);
	itterations = atol(argv[3]);
	cow = atol(argv[4]);
	printf("mmaping %ld anonymous bytes\n", siz); 
	ptr1 = (char *)mmap((void *)0,siz,PROT_READ|PROT_WRITE,MAP_ANONYMOUS|MAP_PRIVATE,-1,0);
	if (ptr1 == (char *)-1) {
		printf("ptr1 = %lx\n", ptr1);
		perror("");
	}
	if (cow) {
		printf("priming parent for child COW faults\n");
		// This will cause the ZFOD faults in the parent & COW faults in the children.
		for (i=ptr1; i<ptr1+siz-1; i+=4096)
			*i=(char)'i';
	}
	printf("forking %ld processes\n", procs);
	k = procs;
	do{
		pid = fork();
		if (pid == -1) {
			printf("fork failure\n");
			exit(-1);
		} else if (!pid) {
			printf("PID %d touching %d pages\n", getpid(), siz/4096);
			// This will ZFOD fault if the parent didnt otherwise it will COW fault.
			for (j=0; j<itterations; j++) {
				for (i=ptr1; i<ptr1+siz-1; i+=4096) {
						*i=(char)'i';
				}
			}
			printf("All done, exiting\n");
			exit(0);
		}
	
	} while(--k);

	while (procs-- && wait(&status));	
}