Free memory from a long vector

[larryyueli]

What I wanted to do is to release the memory used by a vector (say vector<vector<int>>) and I used the swap trick, i.e., v.swap(vector<vector<int>>()).

However, what I observed that the swap trick work well for short vectors but NOT for long ones, for example I tried one vector of length 10,000,000, which took 1.3G in memory, after the swap there is still 1.0G not released.

I learned that this has something to do with the C++ runtime library, my question is that there a way to force the memory to be released by the process? I want to make one process release its memory so that another process can use it.

Below is the code I used for testing.

Thanks advance for any help

#include <iostream>
#include <vector>

using namespace std;

typedef unsigned long long     int64;

int main()
{
    {
        vector<vector<int64>> batch;
        {
            vector<int64> v;
            for (size_t i = 0; i < 12; ++i)
                v.push_back(8000000000);
            for (size_t i = 0; i < 10000000; ++i)
                batch.push_back(v);
        }
        cout << "pause 1" << endl;
        cin.ignore();
        {
            vector<vector<int64>> tmp;
            batch.swap(tmp);
            // I tried several things here.
            //tmp.swap(batch);
            //batch.clear();
            //batch.shrink_to_fit();
            //batch = tmp;
        }
        cout << "pause 2" << endl;
        cin.ignore();
    }
    cout << "pause 3" << endl;
    cin.ignore();
}