我有2种排序算法，合并排序和插入排序。我试图检查它们在执行过程中分配了多少内存，以进行比较。两者都在对1000个元素的数组进行排序，整数在0-999之间。
程序被编译为名为main（merge_sort/main和insertion_sort/main）的二进制文件。所以我正在跑步：
memusage -T ./main
两种算法。
都返回：
heap total: 73728, heap peak: 73728, stack peak: 6144
为什么它们返回相同的？合并排序是否应该分配比插入排序更多的内存？我什至使用memusage正确吗？
我也尝试过使用Valgrind对其进行检查，这对于两个对象也都返回相同的结果：
==26544== HEAP SUMMARY:
==26544== in use at exit: 0 bytes in 0 blocks
==26544== total heap usage: 2 allocs, 2 frees, 73,728 bytes allocated
我的理论是：要么我不知道自己在做什么，
或者排序的列表很小。因此，内存使用情况看起来相同。
代码：
合并排序
/* C program for Merge Sort */
#include<stdlib.h>
#include<stdio.h>
#include<time.h>
// Merges two subarrays of arr[].
// First subarray is arr[l..m]
// Second subarray is arr[m+1..r]
void merge(int arr[], int l, int m, int r)
{
int i, j, k;
int n1 = m - l + 1;
int n2 = r - m;
/* create temp arrays */
int L[n1], R[n2];
/* Copy data to temp arrays L[] and R[] */
for (i = 0; i < n1; i++)
L[i] = arr[l + i];
for (j = 0; j < n2; j++)
R[j] = arr[m + 1+ j];
/* Merge the temp arrays back into arr[l..r]*/
i = 0; // Initial index of first subarray
j = 0; // Initial index of second subarray
k = l; // Initial index of merged subarray
while (i < n1 && j < n2)
{
if (L[i] <= R[j])
{
arr[k] = L[i];
i++;
}
else
{
arr[k] = R[j];
j++;
}
k++;
}
/* Copy the remaining elements of L[], if there
are any */
while (i < n1)
{
arr[k] = L[i];
i++;
k++;
}
/* Copy the remaining elements of R[], if there
are any */
while (j < n2)
{
arr[k] = R[j];
j++;
k++;
}
}
/* l is for left index and r is right index of the
sub-array of arr to be sorted */
void mergeSort(int arr[], int l, int r)
{
if (l < r)
{
// Same as (l+r)/2, but avoids overflow for
// large l and h
int m = l+(r-l)/2;
// Sort first and second halves
mergeSort(arr, l, m);
mergeSort(arr, m+1, r);
merge(arr, l, m, r);
}
}
/* UTILITY FUNCTIONS */
/* Function to print an array */
void printArray(int A[], int size)
{
int i;
for (i=0; i < size; i++)
printf("%d ", A[i]);
printf("\n");
}
/* Driver program to test above functions */
int main()
{
int arr[] = {
397, 326, 157, 581, 198, 158, 107, 479, 919, 288, 118, 14, 384, 389, 354, 905, 648, 24, 639, 279, 846, 896, 901, 491, 827, 502, 119, 520, 544, 688, 433, 542, 280, 834, 574, 739, 168, 714, 367, 547, 555, 616, 71, 583, 77, 372, 380, 414, 80, 828, 671, 900, 710, 852, 810, 471, 493, 832, 310, 579, 605, 174, 19, 576, 162, 695, 635, 851, 265, 48, 536, 228, 754, 300, 610, 272, 619, 825, 770, 147, 9, 813, 525, 135, 768, 654, 889, 446, 910, 678, 432, 172, 618, 41, 839, 589, 304, 484, 765, 357, 427, 617, 75, 683, 930, 593, 341, 149, 733, 27, 556, 474, 987, 156, 501, 665, 370, 523, 142, 420, 114, 798, 989, 382, 543, 879, 294, 305, 684, 331, 443, 383, 625, 647, 780, 811, 34, 621, 744, 842, 150, 938, 301, 495, 965, 392, 634, 358, 570, 789, 266, 242, 709, 278, 932, 57, 952, 475, 984, 136, 133, 637, 734, 207, 697, 362, 344, 332, 89, 529, 188, 164, 124, 317, 103, 257, 514, 364, 356, 203, 112, 831, 867, 644, 815, 452, 456, 260, 291, 90, 13, 21, 160, 217, 251, 459, 213, 110, 455, 56, 753, 127, 349, 884, 434, 982, 224, 410, 104, 540, 640, 973, 486, 945, 201, 166, 99, 535, 229, 725, 361, 483, 190, 743, 998, 409, 159, 102, 55, 219, 720, 33, 971, 859, 335, 887, 538, 363, 557, 696, 11, 951, 51, 845, 231, 723, 569, 63, 903, 185, 406, 505, 833, 309, 49, 599, 788, 511, 990, 196, 324, 803, 247, 970, 440, 504, 627, 205, 656, 308, 948, 690, 551, 819, 988, 608, 67, 519, 907, 510, 603, 256, 597, 880, 893, 214, 95, 270, 915, 179, 298, 378, 550, 953, 717, 321, 992, 863, 796, 868, 604, 152, 368, 15, 284, 17, 925, 808, 799, 841, 946, 974, 450, 546, 682, 91, 666, 402, 283, 736, 567, 679, 125, 299, 319, 762, 849, 785, 264, 797, 623, 401, 689, 140, 461, 171, 454, 624, 853, 724, 191, 130, 86, 451, 87, 109, 38, 61, 413, 348, 289, 829, 969, 670, 528, 588, 937, 766, 885, 237, 823, 592, 184, 73, 239, 643, 180, 10, 195, 277, 787, 431, 562, 390, 338, 146, 638, 85, 424, 652, 2, 631, 685, 405, 35, 387, 912, 333, 740, 692, 769, 66, 554, 565, 926, 223, 322, 826, 657, 858, 703, 1, 986, 312, 246, 31, 577, 323, 145, 439, 375, 39, 170, 106, 478, 978, 716, 254, 756, 37, 360, 350, 463, 269, 52, 64, 386, 509, 997, 429, 379, 655, 916, 878, 553, 794, 807, 197, 16, 840, 947, 860, 920, 963, 70, 183, 572, 763, 192, 729, 340, 238, 209, 469, 151, 167, 292, 303, 129, 847, 749, 4, 218, 216, 924, 215, 784, 243, 394, 836, 782, 476, 268, 78, 54, 590, 81, 908, 23, 704, 428, 778, 976, 680, 211, 622, 131, 273, 236, 487, 416, 767, 854, 870, 255, 837, 336, 611, 958, 233, 991, 3, 764, 83, 7, 541, 244, 792, 790, 0, 407, 418, 812, 334, 32, 872, 883, 537, 518, 72, 293, 886, 220, 866, 42, 730, 929, 891, 126, 470, 686, 329, 28, 568, 563, 659, 186, 706, 923, 497, 942, 844, 850, 492, 783, 715, 415, 153, 120, 448, 496, 468, 398, 620, 369, 373, 629, 79, 835, 711, 750, 311, 738, 346, 881, 121, 911, 50, 612, 498, 395, 955, 490, 774, 944, 506, 584, 664, 445, 173, 524, 561, 252, 713, 359, 771, 595, 96, 458, 956, 967, 422, 507, 177, 515, 342, 488, 759, 274, 275, 385, 816, 983, 306, 263, 830, 897, 760, 82, 426, 5, 698, 200, 981, 276, 559, 613, 154, 532, 735, 84, 345, 909, 94, 202, 302, 580, 508, 44, 134, 374, 898, 100, 993, 116, 712, 943, 646, 552, 975, 800, 6, 824, 328, 318, 960, 245, 708, 548, 403, 60, 931, 499, 676, 88, 894, 465, 921, 817, 693, 591, 957, 818, 721, 596, 649, 935, 261, 747, 391, 917, 314, 296, 460, 376, 412, 227, 240, 139, 871, 776, 691, 513, 93, 606, 531, 464, 694, 977, 108, 69, 259, 466, 417, 58, 737, 786, 43, 707, 933, 307, 74, 719, 653, 327, 746, 913, 262, 922, 731, 199, 494, 804, 877, 873, 732, 285, 727, 47, 210, 927, 914, 194, 758, 602, 582, 566, 941, 598, 809, 672, 966, 258, 137, 961, 902, 467, 92, 105, 316, 29, 234, 781, 675, 286, 226, 353, 857, 777, 472, 68, 985, 480, 330, 250, 248, 282, 962, 838, 176, 208, 40, 175, 178, 281, 396, 444, 436, 560, 521, 895, 366, 377, 586, 578, 212, 641, 232, 687, 571, 876, 585, 117, 101, 862, 701, 934, 939, 968, 189, 53, 677, 573, 869, 113, 642, 65, 607, 143, 979, 645, 856, 352, 20, 522, 249, 355, 148, 22, 473, 742, 98, 347, 419, 477, 705, 674, 757, 899, 430, 489, 425, 949, 726, 950, 123, 667, 399, 297, 594, 650, 587, 503, 141, 442, 748, 221, 775, 500, 339, 668, 400, 45, 814, 516, 663, 996, 772, 882, 230, 267, 722, 404, 821, 204, 755, 12, 702, 435, 822, 315, 630, 673, 848, 438, 482, 408, 928, 512, 371, 779, 626, 235, 527, 462, 904, 651, 661, 411, 752, 36, 980, 761, 485, 855, 241, 222, 287, 46, 802, 801, 206, 453, 111, 874, 295, 59, 628, 806, 290, 575, 600, 337, 728, 995, 138, 609, 875, 193, 30, 658, 558, 76, 481, 890, 745, 615, 132, 614, 795, 393, 351, 741, 564, 805, 457, 313, 545, 632, 964, 381, 25, 533, 26, 633, 62, 530, 751, 517, 936, 791, 820, 155, 940, 365, 843, 8, 918, 662, 225, 681, 388, 187, 660, 144, 793, 773, 181, 421, 161, 423, 447, 169, 994, 669, 700, 163, 526, 999, 959, 437, 449, 888, 271, 954, 18, 253, 320, 892, 864, 718, 865, 601, 699, 972, 549, 115, 441, 128, 861, 539, 165, 534, 325, 636, 122, 97, 182, 906, 343
};
int n = sizeof(arr)/sizeof(arr[0]);
clock_t begin = clock();
/* here, do your time-consuming job */
mergeSort(arr, 0, n-1);
clock_t end = clock();
double time_spent = (double)(end - begin) / CLOCKS_PER_SEC;
printf("Merge: %.10f", time_spent);
printf("\n");
return 0;
}
插入排序
// C program for insertion sort
#include <math.h>
#include <stdio.h>
#include <time.h>
#include <unistd.h>
/* Function to sort an array using insertion sort*/
void insertionSort(int arr[], int n)
{
int i, key, j;
for (i = 1; i < n; i++) {
key = arr[i];
j = i - 1;
/* Move elements of arr[0..i-1], that are
greater than key, to one position ahead
of their current position */
while (j >= 0 && arr[j] > key) {
arr[j + 1] = arr[j];
j = j - 1;
}
arr[j + 1] = key;
}
}
// A utility function to print an array of size n
void printArray(int arr[], int n)
{
int i;
for (i = 0; i < n; i++)
printf("%d ", arr[i]);
printf("\n");
}
/* Driver program to test insertion sort */
int main()
{
int arr[] = {
397, 326, 157, 581, 198, 158, 107, 479, 919, 288, 118, 14, 384, 389, 354, 905, 648, 24, 639, 279, 846, 896, 901, 491, 827, 502, 119, 520, 544, 688, 433, 542, 280, 834, 574, 739, 168, 714, 367, 547, 555, 616, 71, 583, 77, 372, 380, 414, 80, 828, 671, 900, 710, 852, 810, 471, 493, 832, 310, 579, 605, 174, 19, 576, 162, 695, 635, 851, 265, 48, 536, 228, 754, 300, 610, 272, 619, 825, 770, 147, 9, 813, 525, 135, 768, 654, 889, 446, 910, 678, 432, 172, 618, 41, 839, 589, 304, 484, 765, 357, 427, 617, 75, 683, 930, 593, 341, 149, 733, 27, 556, 474, 987, 156, 501, 665, 370, 523, 142, 420, 114, 798, 989, 382, 543, 879, 294, 305, 684, 331, 443, 383, 625, 647, 780, 811, 34, 621, 744, 842, 150, 938, 301, 495, 965, 392, 634, 358, 570, 789, 266, 242, 709, 278, 932, 57, 952, 475, 984, 136, 133, 637, 734, 207, 697, 362, 344, 332, 89, 529, 188, 164, 124, 317, 103, 257, 514, 364, 356, 203, 112, 831, 867, 644, 815, 452, 456, 260, 291, 90, 13, 21, 160, 217, 251, 459, 213, 110, 455, 56, 753, 127, 349, 884, 434, 982, 224, 410, 104, 540, 640, 973, 486, 945, 201, 166, 99, 535, 229, 725, 361, 483, 190, 743, 998, 409, 159, 102, 55, 219, 720, 33, 971, 859, 335, 887, 538, 363, 557, 696, 11, 951, 51, 845, 231, 723, 569, 63, 903, 185, 406, 505, 833, 309, 49, 599, 788, 511, 990, 196, 324, 803, 247, 970, 440, 504, 627, 205, 656, 308, 948, 690, 551, 819, 988, 608, 67, 519, 907, 510, 603, 256, 597, 880, 893, 214, 95, 270, 915, 179, 298, 378, 550, 953, 717, 321, 992, 863, 796, 868, 604, 152, 368, 15, 284, 17, 925, 808, 799, 841, 946, 974, 450, 546, 682, 91, 666, 402, 283, 736, 567, 679, 125, 299, 319, 762, 849, 785, 264, 797, 623, 401, 689, 140, 461, 171, 454, 624, 853, 724, 191, 130, 86, 451, 87, 109, 38, 61, 413, 348, 289, 829, 969, 670, 528, 588, 937, 766, 885, 237, 823, 592, 184, 73, 239, 643, 180, 10, 195, 277, 787, 431, 562, 390, 338, 146, 638, 85, 424, 652, 2, 631, 685, 405, 35, 387, 912, 333, 740, 692, 769, 66, 554, 565, 926, 223, 322, 826, 657, 858, 703, 1, 986, 312, 246, 31, 577, 323, 145, 439, 375, 39, 170, 106, 478, 978, 716, 254, 756, 37, 360, 350, 463, 269, 52, 64, 386, 509, 997, 429, 379, 655, 916, 878, 553, 794, 807, 197, 16, 840, 947, 860, 920, 963, 70, 183, 572, 763, 192, 729, 340, 238, 209, 469, 151, 167, 292, 303, 129, 847, 749, 4, 218, 216, 924, 215, 784, 243, 394, 836, 782, 476, 268, 78, 54, 590, 81, 908, 23, 704, 428, 778, 976, 680, 211, 622, 131, 273, 236, 487, 416, 767, 854, 870, 255, 837, 336, 611, 958, 233, 991, 3, 764, 83, 7, 541, 244, 792, 790, 0, 407, 418, 812, 334, 32, 872, 883, 537, 518, 72, 293, 886, 220, 866, 42, 730, 929, 891, 126, 470, 686, 329, 28, 568, 563, 659, 186, 706, 923, 497, 942, 844, 850, 492, 783, 715, 415, 153, 120, 448, 496, 468, 398, 620, 369, 373, 629, 79, 835, 711, 750, 311, 738, 346, 881, 121, 911, 50, 612, 498, 395, 955, 490, 774, 944, 506, 584, 664, 445, 173, 524, 561, 252, 713, 359, 771, 595, 96, 458, 956, 967, 422, 507, 177, 515, 342, 488, 759, 274, 275, 385, 816, 983, 306, 263, 830, 897, 760, 82, 426, 5, 698, 200, 981, 276, 559, 613, 154, 532, 735, 84, 345, 909, 94, 202, 302, 580, 508, 44, 134, 374, 898, 100, 993, 116, 712, 943, 646, 552, 975, 800, 6, 824, 328, 318, 960, 245, 708, 548, 403, 60, 931, 499, 676, 88, 894, 465, 921, 817, 693, 591, 957, 818, 721, 596, 649, 935, 261, 747, 391, 917, 314, 296, 460, 376, 412, 227, 240, 139, 871, 776, 691, 513, 93, 606, 531, 464, 694, 977, 108, 69, 259, 466, 417, 58, 737, 786, 43, 707, 933, 307, 74, 719, 653, 327, 746, 913, 262, 922, 731, 199, 494, 804, 877, 873, 732, 285, 727, 47, 210, 927, 914, 194, 758, 602, 582, 566, 941, 598, 809, 672, 966, 258, 137, 961, 902, 467, 92, 105, 316, 29, 234, 781, 675, 286, 226, 353, 857, 777, 472, 68, 985, 480, 330, 250, 248, 282, 962, 838, 176, 208, 40, 175, 178, 281, 396, 444, 436, 560, 521, 895, 366, 377, 586, 578, 212, 641, 232, 687, 571, 876, 585, 117, 101, 862, 701, 934, 939, 968, 189, 53, 677, 573, 869, 113, 642, 65, 607, 143, 979, 645, 856, 352, 20, 522, 249, 355, 148, 22, 473, 742, 98, 347, 419, 477, 705, 674, 757, 899, 430, 489, 425, 949, 726, 950, 123, 667, 399, 297, 594, 650, 587, 503, 141, 442, 748, 221, 775, 500, 339, 668, 400, 45, 814, 516, 663, 996, 772, 882, 230, 267, 722, 404, 821, 204, 755, 12, 702, 435, 822, 315, 630, 673, 848, 438, 482, 408, 928, 512, 371, 779, 626, 235, 527, 462, 904, 651, 661, 411, 752, 36, 980, 761, 485, 855, 241, 222, 287, 46, 802, 801, 206, 453, 111, 874, 295, 59, 628, 806, 290, 575, 600, 337, 728, 995, 138, 609, 875, 193, 30, 658, 558, 76, 481, 890, 745, 615, 132, 614, 795, 393, 351, 741, 564, 805, 457, 313, 545, 632, 964, 381, 25, 533, 26, 633, 62, 530, 751, 517, 936, 791, 820, 155, 940, 365, 843, 8, 918, 662, 225, 681, 388, 187, 660, 144, 793, 773, 181, 421, 161, 423, 447, 169, 994, 669, 700, 163, 526, 999, 959, 437, 449, 888, 271, 954, 18, 253, 320, 892, 864, 718, 865, 601, 699, 972, 549, 115, 441, 128, 861, 539, 165, 534, 325, 636, 122, 97, 182, 906, 343,
};
int n = sizeof(arr)/sizeof(arr[0]);
//printf("n: %d", n);
//printf("Unsorted array: ");
//printArray(arr, n);
//printf("\n");
clock_t begin = clock();
/* here, do your time-consuming job */
insertionSort(arr, n);
clock_t end = clock();
double time_spent = (double)(end - begin) / CLOCKS_PER_SEC;
//printf("Sorted array: ");
//printArray(arr, n);
//printf("\n");
printf("Inser: %.10f", time_spent);
printf("\n");
return 0;
}
答案 0 :(得分：1)
您报告的memusage和valgrind结果彼此一致：每个显示总共动态分配了73728个字节。那里应该就让您暂停一下，因为 您的源代码中没有对动态内存分配函数的调用 。这些字节与您的排序功能无关；它们必须来自标准库在其设置代码或您调用的少数库函数之一中执行的分配。
由于memusage和它依赖的libmemusage.so是由glibc提供的，因此我们不希望他们报告glibc的使用情况，实际上，对我而言，他们没有。我无法解释为什么您会看到不同的结果，但是作为一个疯狂的猜测，也许您使用的是glibc和libmemusage.so的不匹配版本。
但是，您可能会说，堆栈使用情况如何？两种方法不应该使用不同数量的堆栈吗？并且他们不应该使用 some 堆栈，而不是注释中报告的0吗？在这里，您必须了解底层的libmemusage是通过包装选定的内存分配函数而不是 all 函数来运行的。对于the memusage docs，它按如下方式计算堆栈使用量：
在第一次调用任何 受监视的 函数之前，堆栈指针 地址（基本堆栈指针）已保存。在每个[受监视的]函数调用之后， 读取实际的堆栈指针地址，并且与基地址的区别 计算堆栈指针。这些差异的最大值就是 堆峰。
（添加了强调。）因此，
memusage仅提供堆栈使用情况的估计，该估计是通过对受监视函数的调用周围的堆栈指针进行采样来完成的。
因此，对于您的特定程序，memusage不会报告有关排序算法的堆栈使用情况的任何信息，因为您的代码不会调用受监视的函数。
您可以通过手动检测代码来解决此问题，以便libmemusage查看其堆栈使用情况。例如，插入
free(malloc(0));
在main()的开头，以确保记录了堆栈使用的最低点，并插入对诸如以下函数的调用：
void usage_instrumentation(void) {
free(malloc(0));
}
进入其他每个功能。为了捕获调用函数的堆栈使用情况，应在main以外的地方使用函数调用； malloc和free应该在main中直接调用以捕获低点 main的用法，以便将该用法包括在最终估算。此外，请在禁用函数内联（可能包括所有优化）的情况下进行编译，以避免此机制被编译器破坏。
如果我这样做，对我来说，memusage报告插入排序的堆栈使用量为4304字节，合并排序的堆栈使用量为8496字节，两者的差值比数组的大小稍大。就像我期望的那样。