#include <sys/mman.h>
#include <sys/types.h>
#include <sys/time.h>
#include <inttypes.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <ctype.h>
#include <string.h>

#define SIZE (1 * 1024 * 1024 * 1024)
#define PAGE_SIZE 4096

int64_t current_time_ms() {
	struct timeval time;
	gettimeofday(&time, NULL);
	int64_t s1 = (int64_t)(time.tv_sec) * 1000;
	int64_t s2 = (time.tv_usec / 1000);
	return s1 + s2;
}

int main(int argc, char* argv[])
{
	void * buf;
	char * ptr;
	size_t size = SIZE, step = PAGE_SIZE;
	int64_t start, cost;

	buf = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
	if (buf ==  MAP_FAILED) {
		printf("mmap failed\n");
	}

	start = current_time_ms();

	for(size_t i = 0; i < size; i += step ) {
		ptr = (char *)(buf + i);
		*ptr = 'a';
	}

	cost = current_time_ms() - start;
	printf("cost:%" PRId64 " ms\n", cost);

	munmap(buf, size);

        return 0;
}