如何知道使用了哪个malloc函数？

Question

如何知道使用了哪个malloc函数？

c++mallocheap-memory

8

据我所知，存在许多不同的malloc实现：

dlmalloc - 通用分配器
ptmalloc2 - glibc
jemalloc - FreeBSD和Firefox
tcmalloc - Google
libumem - Solaris

有没有办法确定在我的（Linux）系统上实际使用了哪个malloc？

我读到“由于ptmalloc2的线程支持，它成为Linux的默认内存分配器。”我有没有办法自己检查这一点？

我问这个问题是因为我似乎无法通过并行化下面代码中的malloc循环来加快速度：

for (int i = 1; i <= 16; i += 1 ) {
    parallelMalloc(i);
}

 void parallelMalloc(int parallelism, int mallocCnt = 10000000) {

    omp_set_num_threads(parallelism);

    std::vector<char*> ptrStore(mallocCnt);

    boost::posix_time::ptime t1 = boost::posix_time::microsec_clock::local_time();

    #pragma omp parallel for
    for (int i = 0; i < mallocCnt; i++) {
        ptrStore[i] = ((char*)malloc(100 * sizeof(char)));
    }

    boost::posix_time::ptime t2 = boost::posix_time::microsec_clock::local_time();

    #pragma omp parallel for
    for (int i = 0; i < mallocCnt; i++) {
        free(ptrStore[i]);
    }

    boost::posix_time::ptime t3 = boost::posix_time::microsec_clock::local_time();


    boost::posix_time::time_duration malloc_time = t2 - t1;
    boost::posix_time::time_duration free_time   = t3 - t2;

    std::cout << " parallelism = "  << parallelism << "\t itr = " << mallocCnt <<  "\t malloc_time = " <<
            malloc_time.total_milliseconds() << "\t free_time = " << free_time.total_milliseconds() << std::endl;
}

这使我得到了一个输出。

 parallelism = 1         itr = 10000000  malloc_time = 1225      free_time = 1517
 parallelism = 2         itr = 10000000  malloc_time = 1614      free_time = 1112
 parallelism = 3         itr = 10000000  malloc_time = 1619      free_time = 687
 parallelism = 4         itr = 10000000  malloc_time = 2325      free_time = 620
 parallelism = 5         itr = 10000000  malloc_time = 2233      free_time = 550
 parallelism = 6         itr = 10000000  malloc_time = 2207      free_time = 489
 parallelism = 7         itr = 10000000  malloc_time = 2778      free_time = 398
 parallelism = 8         itr = 10000000  malloc_time = 1813      free_time = 389
 parallelism = 9         itr = 10000000  malloc_time = 1997      free_time = 350
 parallelism = 10        itr = 10000000  malloc_time = 1922      free_time = 291
 parallelism = 11        itr = 10000000  malloc_time = 2480      free_time = 257
 parallelism = 12        itr = 10000000  malloc_time = 1614      free_time = 256
 parallelism = 13        itr = 10000000  malloc_time = 1387      free_time = 289
 parallelism = 14        itr = 10000000  malloc_time = 1481      free_time = 248
 parallelism = 15        itr = 10000000  malloc_time = 1252      free_time = 297
 parallelism = 16        itr = 10000000  malloc_time = 1063      free_time = 281

- user695652

8

XY问题？你为什么在意？ - SergeyA

1

@SergeyA 我关心这个问题，因为我想确保我使用的malloc支持多线程以提高性能。 - user695652

实质上，所有版本都必须支持多线程，因为现代系统都是多线程的。在您确定存在问题之前，您可能不必担心它。 - Jonathan Leffler

4

在尝试更换分配器之前，您应该对代码进行分析以确定瓶颈出现在哪里。 - Captain Obvlious

1

@ Captain Obvlious我的代码如下：#pragma omp parallel for for (int i = 0; i < mallocCnt; i++) { ptrStore[i] = ((char*)malloc(100 * sizeof(char))); }我使用omp_set_num_threads（parallelism）来改变并行度，其中0 < parallelism < 16。 - user695652

显示剩余4条评论

1个回答

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- uh oh somebody needs a pupper · Accepted Answer

我看到过这样的说法：“由于ptmalloc2支持多线程，它成为了Linux的默认内存分配器。” 我能自己检查一下吗？

glibc在内部使用ptmalloc2，并非最近才开始。无论如何，做起来并不是特别困难，只需执行“getconf GNU_LIBC_VERSION”，然后交叉检查版本，以确定该版本是否使用ptmalloc2即可，但我敢打赌你会浪费时间。

我之所以问是因为我似乎没有通过将我的malloc循环并行化来获得任何加速。将您的示例转换为MVCE（出于简洁起见，在此省略代码），并使用“g++ -Wall -pedantic -O3 -pthread -fopenmp”进行编译，在此处使用“g++ 5.3.1”的结果如下。

使用OpenMP：

 parallelism = 1     itr = 10000000  malloc_time = 746   free_time = 263
 parallelism = 2     itr = 10000000  malloc_time = 541   free_time = 267
 parallelism = 3     itr = 10000000  malloc_time = 405   free_time = 259
 parallelism = 4     itr = 10000000  malloc_time = 324   free_time = 221
 parallelism = 5     itr = 10000000  malloc_time = 330   free_time = 242
 parallelism = 6     itr = 10000000  malloc_time = 287   free_time = 244
 parallelism = 7     itr = 10000000  malloc_time = 257   free_time = 226
 parallelism = 8     itr = 10000000  malloc_time = 270   free_time = 225
 parallelism = 9     itr = 10000000  malloc_time = 253   free_time = 225
 parallelism = 10    itr = 10000000  malloc_time = 236   free_time = 226
 parallelism = 11    itr = 10000000  malloc_time = 225   free_time = 239
 parallelism = 12    itr = 10000000  malloc_time = 276   free_time = 258
 parallelism = 13    itr = 10000000  malloc_time = 241   free_time = 228
 parallelism = 14    itr = 10000000  malloc_time = 254   free_time = 225
 parallelism = 15    itr = 10000000  malloc_time = 278   free_time = 272
 parallelism = 16    itr = 10000000  malloc_time = 235   free_time = 220

23.87 user 
2.11 system 
0:10.41 elapsed 
249% CPU

没有OpenMP：

 parallelism = 1     itr = 10000000  malloc_time = 748   free_time = 263
 parallelism = 2     itr = 10000000  malloc_time = 344   free_time = 256
 parallelism = 3     itr = 10000000  malloc_time = 751   free_time = 254
 parallelism = 4     itr = 10000000  malloc_time = 339   free_time = 262
 parallelism = 5     itr = 10000000  malloc_time = 748   free_time = 253
 parallelism = 6     itr = 10000000  malloc_time = 330   free_time = 256
 parallelism = 7     itr = 10000000  malloc_time = 734   free_time = 260
 parallelism = 8     itr = 10000000  malloc_time = 334   free_time = 259
 parallelism = 9     itr = 10000000  malloc_time = 750   free_time = 256
 parallelism = 10    itr = 10000000  malloc_time = 339   free_time = 255
 parallelism = 11    itr = 10000000  malloc_time = 743   free_time = 267
 parallelism = 12    itr = 10000000  malloc_time = 342   free_time = 261
 parallelism = 13    itr = 10000000  malloc_time = 739   free_time = 252
 parallelism = 14    itr = 10000000  malloc_time = 333   free_time = 252
 parallelism = 15    itr = 10000000  malloc_time = 740   free_time = 252
 parallelism = 16    itr = 10000000  malloc_time = 330   free_time = 252

13.38 user 
4.66 system 
0:18.08 elapsed 
99% CPU

并行化似乎比普通执行快了约8秒钟。还不信？好吧，我已经获取了 dlmalloc，运行 make 命令生成 libmalloc.a。我的新命令是 g++ -Wall -pedantic -O3 -pthread -fopenmp -L$HOME/Development/test/dlmalloc/lib test.cpp -lmalloc

使用 OpenMP:

parallelism = 1  itr = 10000000  malloc_time = 814   free_time = 277

我在37秒后按下了CTRL-C。

没有使用OpenMP：

 parallelism = 1     itr = 10000000  malloc_time = 772   free_time = 271
 parallelism = 2     itr = 10000000  malloc_time = 780   free_time = 272
 parallelism = 3     itr = 10000000  malloc_time = 783   free_time = 272
 parallelism = 4     itr = 10000000  malloc_time = 792   free_time = 277
 parallelism = 5     itr = 10000000  malloc_time = 813   free_time = 281
 parallelism = 6     itr = 10000000  malloc_time = 800   free_time = 275
 parallelism = 7     itr = 10000000  malloc_time = 795   free_time = 277
 parallelism = 8     itr = 10000000  malloc_time = 790   free_time = 273
 parallelism = 9     itr = 10000000  malloc_time = 788   free_time = 277
 parallelism = 10    itr = 10000000  malloc_time = 784   free_time = 276
 parallelism = 11    itr = 10000000  malloc_time = 786   free_time = 284
 parallelism = 12    itr = 10000000  malloc_time = 807   free_time = 279
 parallelism = 13    itr = 10000000  malloc_time = 791   free_time = 277
 parallelism = 14    itr = 10000000  malloc_time = 790   free_time = 273
 parallelism = 15    itr = 10000000  malloc_time = 785   free_time = 276
 parallelism = 16    itr = 10000000  malloc_time = 787   free_time = 275

6.48 user 
11.27 system 
0:17.81 elapsed 
99% CPU

相当大的差异。我怀疑问题在于您更复杂的代码，或者您的基准测试有问题。