#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <unistd.h>
#include <string.h>

#ifndef MADV_PAGEOUT
#define MADV_PAGEOUT 21
#endif

/* 1G size testing */
static int SIZE = 1024UL*1024*1024;
//static int SIZE = 2UL*1024*1024;
//static int SIZE = 64*1024;

int main(void)
{
	pid_t pid;
	char *shared_memory = mmap(NULL, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);

	if (shared_memory == MAP_FAILED) {
		perror("mmap failed");
		exit(EXIT_FAILURE);
	}

	//populate the shmem
	memset(shared_memory, 0xaa, SIZE);

	/* create child */
	pid = fork();
	if (pid < 0) {
		perror("fork failed");
		exit(EXIT_FAILURE);
	} else if (pid == 0) {
		printf("Child process sees shared_memory[0x%lx] = %d\n", (unsigned long)shared_memory, *shared_memory);
		(*shared_memory)++;
		printf("Child process incremented shared_memory to %d\n", *shared_memory);
		exit(0);
	} else {
		/* parent:wait for child to complete */
		wait(NULL);
		printf("Parent process sees shared_memory = %d\n", *shared_memory);
		(*shared_memory)++;
		printf("Parent process incremented shared_memory to %d\n", *shared_memory);
	}

	if (madvise(shared_memory, SIZE, MADV_PAGEOUT)) {
		perror("madvise(MADV_HUGEPAGE)");
		exit(1);
	}

	if (madvise(shared_memory, SIZE, MADV_PAGEOUT)) {
		perror("madvise(MADV_HUGEPAGE)");
		exit(1);
	}

	memset(shared_memory, 0, SIZE);

	if (munmap(shared_memory, SIZE) == -1) {
		perror("munmap failed");
		exit(EXIT_FAILURE);
	}
	return 0;
}