Why mmap cannot allocate memory?

Question

I ran the program with root priviledge but it keeps complaining that mmap cannot allocate memory. Code snippet is below:

#define PROTECTION (PROT_READ | PROT_WRITE)
#define LENGTH (4*1024)

#ifndef MAP_HUGETLB
#define MAP_HUGETLB 0x40000
#endif

#define ADDR (void *) (0x0UL)
#define FLAGS (MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB)

int main (int argc, char *argv[]){
...
  // allocate a buffer with the same size as the LLC using huge pages
  buf = mmap(ADDR, LENGTH, PROTECTION, FLAGS, 0, 0);
  if (buf == MAP_FAILED) {
    perror("mmap");
    exit(1);
  }
...}

Hardware: I have 8G RAM. Processor is ivybridge

Uname output:

Linux mymachine 3.13.0-43-generic #72-Ubuntu SMP Mon Dec 8 19:35:06 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

EDIT 1: The output of perror

mmap: Cannot allocate memory

Also added one line to print errno

printf("something is wrong: %d\n", errno);

But the output is:

something is wrong: 12

EDIT 2: The huge tlb related information from /proc/meminfo

HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB

Answer 1

Well, as Documentation/vm/hugetlspage.txt suggested, do

echo 20 > /proc/sys/vm/nr_hugepages

solved the problem. Tested on ubuntu 14.04. Check Why I can't map memory with mmap also.