MMAP是否总是返回较高地址 [英] Does mmap always return higher address

问题描述

确实 MMAP （与MAP_ANONYMOUS叫，就是分配内存）总是返回更高的内存地址超过previous电话吗？如果不是这样，有什么办法让它返回一个更高的地址总是？

Does mmap (when called with MAP_ANONYMOUS, that is, for allocating memory) always return higher memory address than a previous call? If not so, Is there any way to make it return a higher address always?

推荐答案

不一定，至少不会根据它的定义。

Not necessarily, at least not according to its definition.

和我相信，随着 ASLR 是可能发生的上限地址没有更多的可用，所以 MMAP 必须选择一些较低地址范围。

And I would believe that with ASLR it could happen that upper addresses are no more available, so mmap has to choose some lower address range.

显然，在32位处理器（安培;内核）的存储空间，可以几乎占满，所以要求一个大的 MMAP -ed范围时，内核应该找到一个其中配合，并且可以在任何地方。

Obviously, on 32 bits processors (& kernels) the memory space could be nearly filled, so when asking for a big mmap-ed range the kernel should find one which fits, and that could be anywhere.

如果你想有一个单调的方向，使用 SBRK （但我真的不推荐使用它）。

If you want a monotone direction, use sbrk (but I really recommend against using it).

另一种可能性是，以pre-分配一个非常大的量使用（例如数TB）的地址空间 MMAP 与 MAP_NORESERVE 在程序初始化，并调用 MMAP 与 MAP_FIXED 里面那个范围再次得到真正可用空间（以更易于管理的数据块，比如几十兆）。

Another possibility could be to pre-allocate a very large amount (e.g. several terabytes) of address space using mmap with MAP_NORESERVE at program initialization, and call mmap with MAP_FIXED inside that range again to get the really usable space (in more manageable chunks, e.g. dozens of megabytes).

@MetallicPriest：你真的应该鼓励，并解释更您的问题。有那么神秘和古怪（甚至我无法猜测所有的上下文中），这是不是很有趣的回答。

@MetallicPriest: you really should motivate and explain much more your questions. There are so mysterious and weird (and even I cannot guess all the context) that it is not very fun to answer them.

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