Generally, the heap is not shrunk after each free. Instead, the malloc() implementation keeps freed memory around for a subsequent allocation. Only when the size of the heap is significantly larger than the amount of allocated memory does malloc() shrink the data segment. A large allocation, however, can prevent this shrinkage.

Consequently, for large allocations, glibc does not use the heap. Instead, glibc creates an anonymous memory mapping to satisfy the allocation request.

【 在 confusing 的大作中提到: 】
: 外行救助。
: container分配的内存如何才能彻底释放？
: 测试了很多办法，vector，set，map一类的container，不论是clear，erase，还是swap，
: ...................
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