导致malloc()在CentOS上返回NULL

在Linux Kernel Memory之后：

//在此处保存您的工作并记下您当前的overcommit_ratio值

# echo 2 > overcommit_memory
# echo 1 > overcommit_ratio

这会将VM_OVERCOMMIT_MEMORY设置为2,表示不会过度使用overcommit_ratio,设置为1(即不会过度使用)

Null malloc演示

#include <stdio.h>
#include <stdlib.h>

int main(int argc,char *argv[])
{
  void *page = 0; int index;
  void *pages[256];
  index = 0;
  while(1)
  {
    page = malloc(1073741824); //1GB
    if(!pagE)break;
    pages[index] = page;
    ++index;
    if(index >= 256)break;
  }
  if(index >= 256)
  {
    printf("allocated 256 pages\n");
  }
  else
  {
    printf("memory Failed at %d\n",indeX);
  }
  while(index > 0)
  {
    --index;
    free(pages[index]);
  }
  return 0;
}

产量

$cat /proc/sys/vm/overcommit_memory 
0
$cat /proc/sys/vm/overcommit_ratio 
50
$./code/stackoverflow/test-memory 
allocated 256 pages
$su
# echo 2 > /proc/sys/vm/overcommit_memory 
# echo 1 > /proc/sys/vm/overcommit_ratio 
# exit
exit
$cat /proc/sys/vm/overcommit_memory 
2
$cat /proc/sys/vm/overcommit_ratio 
1
$./code/stackoverflow/test-memory 
memory Failed at 0

记得将你的overcommit_memory恢复为0和overcommit_ratio,如上所述