c - 为什么 mmap 不能分配内存？

Question

我以 root 权限运行程序，但它一直提示 mmap 无法分配内存。代码片段如下:

#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);
  }
...}

硬件:我有 8G 内存。处理器是ivybridge

Uname 输出:

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

编辑 1:错误的输出

mmap: Cannot allocate memory

还加了一行打印errno

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

但是输出是:

something is wrong: 12

编辑 2:来自/proc/meminfo 的大量 tlb 相关信息

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

Answer 1

嗯，作为Documentation/vm/hugetlspage.txt建议，做

echo 20 > /proc/sys/vm/nr_hugepages

解决了这个问题。在 ubuntu 14.04 上测试。检查Why I can't map memory with mmap还有。