/* gcc -Wall -o memdirty memdirty.c */
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

static void usage(const char *prog, FILE * out)
{
	fprintf(out, "usage: %s allocsize\n", prog);
	fprintf(out, " allocsize is kbytes, or number[KMGP] (P = pages)\n");
	exit(out == stderr);
}

int main(int argc, char *argv[])
{
	long long kbtotal = 0, pages, i;
	unsigned offset;
	char *mem, *tmp;

	if (argc == 2) {
		char *end = NULL;
		kbtotal = strtoull(argv[1], &end, 0);

		switch (*end) {
		case 'g':
		case 'G':
			kbtotal *= 1024;
		case 'm':
		case 'M':
			kbtotal *= 1024;
		case '\0':
		case 'k':
		case 'K':
			break;
		case 'p':
		case 'P':
			kbtotal *= 4;
			break;
		default:
			usage(argv[0], stderr);
			break;
		}
	}

	if (argc != 2 || kbtotal == 0)
		usage(argv[0], stderr);

	pages = kbtotal / 4;
	errno = 0;
	printf("[%d] allocating %lld kbytes, %lld pages\n", getpid(), kbtotal, pages);
	mem = calloc(pages, 4096);
	perror("calloc");
	if (mem == NULL)
		exit(1);

	offset = 0;
	while (1) {
		for (i = 0; i < pages; i++) {
			tmp = (mem + (i * 4096)) + (offset++ & (4096 - 1));
			*tmp = *tmp + 1;
		}
	}
	return 0;
}