performance problems cause by ptmalloc?

Question

I'm testing for std::forward_list sort performance, generate 1000000 random numbers and insert to std::forward_list, sort for 5 times

#include <forward_list>
#include <chrono>
#include <random>
#include <iostream>
#include <vector>

int main()
{
    std::random_device rd;
    std::mt19937 gen(rd());
    std::uniform_int_distribution<int> dis(-100000000, 100000000);
    std::vector<int> v;
    for (int i = 0; i < 1000000; ++i) {
        v.push_back(dis(gen));
    }
    std::forward_list<int> *list;
    for (int j = 0; j < 5; ++j) {
        auto list = new std::forward_list<int>();
        for (auto it = v.begin(); it != v.end(); ++it) {
            list->insert_after(list->cbefore_begin(), *it);
        }
        auto start = std::chrono::steady_clock::now();
        list->sort();
        auto end = std::chrono::steady_clock::now();
        std::chrono::duration<double> diff = end - start;
        std::cout << diff.count() << " s\n";
        delete list;
    }
}

Compile this code with g++ test2.cpp -o test2 -O2 and run, get output

0.994629 s
3.01309 s
2.98853 s
2.99701 s
3.01637 s

If use tcmalloc, compile this code with g++ test2.cpp /usr/local/lib/libtcmalloc_minimal.a -o test2 -O2 and run, get output

0.551351 s
0.550282 s
0.590626 s
0.613431 s
0.559123 s

If delete code delete list;, compile with g++ test2.cpp -o test2 -O2 and run, get output

0.893076 s
0.952251 s
0.95971 s
0.931195 s
0.922877 s

So I think the tcmalloc may cause some performance problems?