/* anoncost.c - first-touch cost per page for different kinds of anonymous memory. usage: anoncost MB */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ipc.h>
#include <sys/shm.h>
static double now(void){struct timeval tv;gettimeofday(&tv,0);return tv.tv_sec+tv.tv_usec/1e6;}
static void touch(const char *what, char *p, long n, long pg){ long i; double t0=now(); for(i=0;i<n;i++) p[i*pg]=1; printf("%-28s %6.1f us/page\n", what, (now()-t0)*1e6/n); }
int main(int argc,char**argv){ long mb=atol(argv[1]), b=mb<<20, pg=4096, n=b/pg; char *p; int fd, id;
  p=malloc(b); touch("malloc (sbrk heap)",p,n,pg); free(p);
  p=mmap(0,b,PROT_READ|PROT_WRITE,MAP_ANONYMOUS|MAP_PRIVATE,-1,0); touch("mmap anon private",p,n,pg); touch("  retouch",p,n,pg); munmap(p,b);
  p=mmap(0,b,PROT_READ|PROT_WRITE,MAP_ANONYMOUS|MAP_SHARED,-1,0); touch("mmap anon shared",p,n,pg); munmap(p,b);
  fd=open("/dev/zero",O_RDWR); p=mmap(0,b,PROT_READ|PROT_WRITE,MAP_PRIVATE,fd,0); if(p!=MAP_FAILED){touch("mmap /dev/zero private",p,n,pg); munmap(p,b);} else printf("mmap /dev/zero: failed\n");
  id=shmget(IPC_PRIVATE,b,IPC_CREAT|0600); p=shmat(id,0,0); shmctl(id,IPC_RMID,0); touch("shmat",p,n,pg); shmdt(p);
  p=malloc(b); touch("malloc again",p,n,pg);
  return 0; }