为什么 C 语言中的 malloc 函数分配的内存比机器配置多？

问：

我在 C 中使用 malloc 函数分配内存，但我遇到了一个奇怪的问题，我对此感到困惑。

以下是程序代码：

#include <stdio.h>
#include <stdlib.h>

#define _1M (1024 * 1024)

// TODO stackOverFlow question
int main(int c, char *v[]) {

    size_t max_allocatable_mem;
    long i = 1;
    char *addr = NULL;

    while (1) {

        max_allocatable_mem = _1M * i;
        addr = malloc(max_allocatable_mem);

        if (addr) {
            printf("allocatable % 16ld M\n", i++);
            free(addr);
        } else {
            printf("can not be allocated % 16ld M\n", i--);
            break;
        }

    }

    printf("\nmax_allocatable_mem = %ld M\n\n", i);

    size_t small_mem_block = max_allocatable_mem / 10;

    for (i=0; i<20; i++) {
        addr = malloc(small_mem_block);
        if (addr) {
            printf("starting address < %p >  capacity < %lu bytes >\n", addr, small_mem_block);
        } else {
            break;
        }
    }

    return 0;
}

程序最初使用 malloc 函数分配最大内存，然后记录可以分配的最大内存。然后，进行小内存的分配。每次分配的小内存是最大可分配内存的十分之一。连续分配 20 次，每次 malloc 都能返回一个特定的内存地址。这样，以后分配的小内存加起来就是程序最初可以分配的最大内存的两倍。

以下是在我的计算机上执行此代码的结果的输出：

allocatable             1332 M
allocatable             1333 M
allocatable             1334 M
allocatable             1335 M
allocatable             1336 M
can not be allocated             1337 M

max_allocatable_mem = 1336 M

starting address < 0x7f8787a4c010 >  capacity < 140194611 bytes >
starting address < 0x7f877f498010 >  capacity < 140194611 bytes >
starting address < 0x7f8776ee4010 >  capacity < 140194611 bytes >
starting address < 0x7f876e930010 >  capacity < 140194611 bytes >
starting address < 0x7f876637c010 >  capacity < 140194611 bytes >
starting address < 0x7f875ddc8010 >  capacity < 140194611 bytes >
starting address < 0x7f8755814010 >  capacity < 140194611 bytes >
starting address < 0x7f874d260010 >  capacity < 140194611 bytes >
starting address < 0x7f8744cac010 >  capacity < 140194611 bytes >
starting address < 0x7f873c6f8010 >  capacity < 140194611 bytes >
starting address < 0x7f8734144010 >  capacity < 140194611 bytes >
starting address < 0x7f872bb90010 >  capacity < 140194611 bytes >
starting address < 0x7f87235dc010 >  capacity < 140194611 bytes >
starting address < 0x7f871b028010 >  capacity < 140194611 bytes >
starting address < 0x7f8712a74010 >  capacity < 140194611 bytes >
starting address < 0x7f870a4c0010 >  capacity < 140194611 bytes >
starting address < 0x7f8701f0c010 >  capacity < 140194611 bytes >
starting address < 0x7f86f9958010 >  capacity < 140194611 bytes >
starting address < 0x7f86f13a4010 >  capacity < 140194611 bytes >
starting address < 0x7f86e8df0010 >  capacity < 140194611 bytes >

为什么连续分配多个小内存的容量加起来可以达到多个分配最大内存的容量？ 会不会是掉期的影响？但是我的电脑上的 Swap 已关闭。

[root@ps-5 ~]# free
              total        used        free      shared  buff/cache   available
Mem:        1881820      434676      462456         632      984688     1288636
Swap:             0           0           0

我希望能得到帮助。

谢谢大家。