mincore.c

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

#define PAGE_SIZE (4096)
static const int size = 100 * PAGE_SIZE;

void runParent(int fd) {
  sleep(1);
  printf("begin mincore\n");
  void* memory = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  int page_count = (size + PAGE_SIZE - 1) / PAGE_SIZE;
  char* vec = (char*)malloc(page_count);
  mincore(memory, size, vec);
  int resident_page_count = 0;
  int i = 0;
  for (i = 0; i < page_count; i++) {
    resident_page_count += vec[i] & 1;
  }
  printf("end mincore\n");
  printf("resident_page_count: %d\n", resident_page_count);
}

void runChild(int fd) {
  printf("begin mmap\n");
  char* memory = (char*)mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  int i = 0;
  // Access pages to use physical memory:                                                                                                                                                                                                                                                                                                                                  
  /*for (i = 0; i < size; i++) {                                                                                                                                                                                                                                                                                                                                           
    memory[i] = 0x01;                                                                                                                                                                                                                                                                                                                                                      
  }*/
  printf("end mmap: %p\n", memory);
  sleep(3);
}

int main() {
  int fd = open("./sharedmemory", O_CREAT | O_TRUNC | O_RDWR, 0666);
  printf("fd: %d\n", fd);
  ftruncate(fd, size);
  pid_t pid = fork();
  if (pid == 0) {
    runChild(fd);
    return 0;
  }
  runParent(fd);
  return 0;
}