#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 unsigned long SIZE = 10UL*1024*1024*1024;
//static int SIZE = 2UL*1024*1024;
//static int SIZE = 64*1024;

static void child_swapin_shmem(char *shared_memory)
{
	char *second_memory;
	int i;

	//swap in shmem without aligned 64k
	second_memory = shared_memory + 4096 * 2;
	for (i = 0; i < SIZE; i += 4096 * 16) {
		*(second_memory + i) = (char)i;
		*(second_memory + i + 4096 * 4) = (char)i;
		*(second_memory + i + 4096 * 9) = (char)i;
	}
}

int main(void)
{
	pid_t pid;
	char *second_memory;
	int i;
	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);

	/* swapout all shmem */
	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);
        }

	/* 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)++;
		child_swapin_shmem(shared_memory);
		printf("Child process incremented shared_memory to %d\n", *shared_memory);
		exit(0);
	} else {
		printf("Parent process sees shared_memory = %d\n", *shared_memory);
		(*shared_memory)++;
		printf("Parent process incremented shared_memory to %d\n", *shared_memory);
	}

	//swap in shmem without aligned 64k
	second_memory = shared_memory + 4096 * 3;
	for (i = 0; i < SIZE; i += 4096 * 16) {
		*(second_memory + i) = (char)i;
		*(second_memory + i + 4096 * 3) = (char)i;
		*(second_memory + i + 4096 * 10) = (char)i;
	}

	/* parent:wait for child to complete */
	wait(NULL);

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