C中的内存使用问题

请帮忙 ：） 操作系统：Linux

其中“sleep(1000);”中，此时“top(显示Linux任务)”给我写了7.7%MEM使用。 valgrind：未发现内存泄漏。

我明白，写得正确，所有 malloc 结果都是 NULL。 但是为什么这次“睡眠”我的程序没有减少内存？缺少什么？

抱歉我的英语不好，谢谢

~ # tmp_soft
For : Is it free??  no
Is it free??  yes
For 0 
For : Is it free??  no
Is it free??  yes
For 1 
END : Is it free??  yes
END 

出于充分的理由，几乎没有内存分配器将块返回给操作系统

内存只能以页为单位从程序中删除，即使这样也不太可能被观察到。

calloc(3) and malloc(3) do interact with the kernel to get memory, if necessary. But very, very few implementations of free(3) ever return memory to the kernel¹, they just add it to a free list that calloc() and malloc() will consult later in order to reuse the released blocks. There are good reasons for this design approach.

即使 free() 想要将内存返回给系统，它也需要至少一个连续的内存页才能让内核真正保护该区域，因此释放一小块只会导致保护更改（如果它是）这last页面中的小块。

操作原理

因此 malloc(3) 在需要时从内核获取内存，最终以离散页倍数为单位。这些页面根据程序的需要进行划分或合并。 malloc 和 free 合作维护一个目录。它们在可能的情况下合并相邻的空闲块，以便能够提供大块。目录可能涉及也可能不涉及使用已释放块中的内存来形成链接列表。 （替代方案是更共享内存和分页友好，并且它涉及专门为目录分配内存。）即使特殊和可选的调试代码被编译成，Malloc 和 free 也几乎没有能力强制访问各个块该程序。

^{1. The fact that very few implementations of free() attempt to return memory to the system is not at all due to the implementors slacking off.}

^{Interacting with the kernel is much slower than simply executing library code, and the benefit would be small. Most programs have a steady-state or increasing memory footprint, so the time spent analyzing the heap looking for returnable memory would be completely wasted. Other reasons include the fact that internal fragmentation makes page-aligned blocks unlikely to exist, and it's likely that returning a block would fragment blocks to either side. Finally, the few programs that do return large amounts of memory are likely to bypass malloc() and simply allocate and free pages anyway.}