hugepages allocated by mmap is slower than posix_memalign - huge-pages

Question

#include <stdlib.h>
#include <stdio.h>
#include <strings.h>
#include <sys/mman.h>
#include <time.h>
#define HUGEPAGE 2048*1024
void *normal_malloc(int len)
{
void *ptr = malloc(len);
bzero(ptr, len);
return ptr;
}
void *trans_malloc(int len)
{
void *ptr = NULL;
int ret = posix_memalign(&ptr, HUGEPAGE, len);
if(ret) perror("posix_memalign");
ret = madvise(ptr, len, MADV_HUGEPAGE);
bzero(ptr, len);
return ptr;
}
void *mmap_malloc(int len)
{
void *ptr = mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_HUGETLB, -1,0);
return ptr;
}
int main(int argc, char **argv)
{
char *ptr = NULL;
int len = HUGEPAGE*256;
srand(time(NULL));
switch(argc){
case 1: ptr = normal_malloc(len);break;
case 2: ptr = trans_malloc(len);break;
case 3: ptr = mmap_malloc(len); break;
}
long j = 0;
for(int i=0;i<len;i++){
j += ptr[rand()%len];
}
return 0;
}
I use normal malloc and posix_memalign and mmap to test performance.
My test result is :
malloc cost about 29.7s, posix_memalign cost about 23.5s, and mmap is very near with malloc.
Both posix_memalign and mmap uses hugepages. Why one has obvious improvement, the other not? Do I use mmap in the wrong way?
I don't do bzero for mmap since the man pages says "its contents are initialized to zero".