如何使用进程的 memory 用法检查 memory 泄漏？

Question

int ParseLine(char* line){
   int i = strlen(line);
   const char* p = line;
   while(*p < '0' || *p > '9') p++;    // Search until a number is found.
   line[i - 3] = '\0'; // Remove " kB"
   i = atoi(p);
   return i;
}

int GetCurrentVirtualMem(){
   std::string cur_proc;
   cur_proc = "/proc/" + std::to_string((int)getpid()) + "/status";

   FILE* fs = fopen(cur_proc.c_str(), "r");
   int result = -1;
   char line[128];

   while(fgets(line, 128, fs) != NULL){
       if(strncmp(line, "VmSize:", 7) == 0){
           result = ParseLine(line);
           break;
       }
   }
   fclose(fs);
   fs = NULL;  //garly modify, for test memory problem

   return result;
}

int GetCurrentMem(){
   std::string cur_proc;
   cur_proc = "/proc/" + std::to_string((int)getpid()) + "/status";

   FILE* fs = fopen(cur_proc.c_str(), "r");
   int result = -1;
   char line[128];

   while(fgets(line, 128, fs) != NULL){
       if(strncmp(line, "VmRSS:", 6) == 0){
           result = ParseLine(line);
           break;
       }
   }
   fclose(fs);
   fs = NULL;  //garly modify, for test memory problem
   return result;
}

I'm trying to check memory leaks but I don't understand physical memory and virtual memory clearly. So I just printed both using the functions above.

float curr_mem = (float)GetCurrentMem() / 1000;
float curr_vir_mem = (float)GetCurrentVirtualMem() / 1000;
std::cout << "Using memory(" << std::to_string((int)getpid()) << "): " << curr_mem << ", " << curr_vir_mem << std::endl;

If I check the changes of physical memory or virtual memory, which one should I take a look at? Both? or one of them?

And I found that even if there are no memory leaks the memory values are changed.

int main(int argc, char *argv[])
{
   QApplication a(argc, argv);

   float prev_mem = 0;
   float prev_vir_mem = 0;
   while(true){

       int* mem_leak = new int[100];


       float curr_mem = (float)GetCurrentMem() / 1000;
       float curr_vir_mem = (float)GetCurrentVirtualMem() / 1000;

       if(prev_mem != curr_mem || prev_vir_mem != curr_vir_mem){
           prev_mem = curr_mem ;
           prev_vir_mem = curr_vir_mem;

           std::cout << "Using memory(" << std::to_string((int)getpid()) << "): " << curr_mem << ", " << curr_vir_mem << std::endl;
       }

       delete[] mem_leak;
   }
   return 0;
}

After an hour of running the code above, it showed the changes in the memory

Using memory(3303): 28.296, 250.788 
Using memory(3303): 28.652, 250.788 
Using memory(3303): 28.916, 250.788

So is this method fine to check memory leak or not? I used "Valgrind" but it didn't show any memory leak message from my code(not the above code. It is too huge to upload here. It is over 30000 lines.). But it showed memory changes in the long-term running test(about 1-week).

Please let me know how to check memory leaks correctly without using other software(such as Valgrind).

Answer 1

If I understand you correctly you want to check for memory leaks on Linux using a process image from an process that has not been instrumented in any way.

https://github.com/vmware/chap (free open source) does this.

First you gather a core:

echo 0x37 > /proc/<pid-of-your-process>/coredump_filter
gcore <pid-of-your-process>

Then you open the core in chap:

chap <core-just-created-by-gcore>

To check for the classic kind of leak (objects that can no longer be reached) you can use the following commands from the chap prompt:

count leaked

That tells you how many objects were leaked.

describe leaked /showUpTo 100

That describes each leaked object, gives a hex dump of up to 0x100 bytes of each object and gives you the count at the end.

Various other commands are available but I don't want to repeat the user's manual.