/* twofault.c - read-only first touch, then first write, per kind of memory. usage: twofault MB */
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/mman.h>
static double now(void){struct timeval tv;gettimeofday(&tv,0);return tv.tv_sec+tv.tv_usec/1e6;}
static volatile int sink;
static void rw(const char *what, char *p, long n){ long i; double t0, tr, tw;
  t0=now(); for(i=0;i<n;i++) sink += p[i*4096]; tr=now()-t0;
  t0=now(); for(i=0;i<n;i++) p[i*4096]=1; tw=now()-t0;
  printf("%-22s read-first %6.1f us/page   then write %6.1f us/page\n", what, tr*1e6/n, tw*1e6/n); }
int main(int argc,char**argv){ long mb=atol(argv[1]), b=mb<<20, n=b/4096; char *p;
  p=malloc(b); rw("malloc heap",p,n);
  p=mmap(0,b,PROT_READ|PROT_WRITE,MAP_ANONYMOUS|MAP_PRIVATE,-1,0); rw("mmap anon private",p,n); munmap(p,b);
  p=mmap(0,b,PROT_READ|PROT_WRITE,MAP_ANONYMOUS|MAP_SHARED,-1,0); rw("mmap anon shared",p,n); munmap(p,b);
  return 0; }