#include <unistd.h>
#include <stdio.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define SIZE (256 * 1024 * 1024)

int main(int argc, char **argv)
{
	char *ptr;
	int fd, i;

	if (argc < 2) {
		printf("Usage: %s <filename>\n", argv[0]);
		return 1;
	}

	fd = open(argv[1], O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
	if (fd < 0) {
		perror("Failed to open file");
		return 1;
	}

	if (ftruncate(fd, SIZE)) {
		perror("Failed to truncate to full size");
		return 1;
	}

	ptr = mmap(NULL, SIZE, PROT_WRITE, MAP_SHARED, fd, 0);
	if (ptr == MAP_FAILED) {
		perror("Failed to mmap");
		return 1;
	}

	/* touch each page */
	for (i = 0; i < SIZE; i += 4096)
		ptr[i] = 1;

	/* Uncommenting the below line masks the problem */
	/* msync(ptr, SIZE, MS_SYNC); */

	if (munmap(ptr, SIZE)) {
		perror("Failed to munmap");
		return 1;
	}

	close(fd);

	return 0;
}