mmap 是否总是返回更高的地址 [英] Does mmap always return higher address

问题描述

mmap(使用 MAP_ANONYMOUS 调用时，即分配内存时)是否总是返回比前一次调用更高的内存地址?如果不是这样，有没有办法让它总是返回一个更高的地址?

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，至少不是根据其定义.

Not necessarily, at least not according to its definition.

而且我相信使用 ASLR 可能会发生上层地址不再可用的情况，所以 mmap 必须选择一些较低的地址范围.

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(& 内核)上，内存空间可能几乎被填满，所以当请求一个大的 mmap-ed 范围时，内核应该找到一个适合的，并且可以随时随地.

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.

如果你想要一个单调的方向，使用 sbrk(但我真的不建议使用它).

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

另一种可能是在程序初始化时使用mmap 和MAP_NORESERVE 预先分配大量(例如几TB)的地址空间，并调用mmap 和 MAP_FIXED 再次位于该范围内以获得真正可用的空间(以更易于管理的块，例如几十兆字节).

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:你真的应该激励和解释更多你的问题.有如此神秘和怪异(甚至我无法猜测所有上下文)，回答它们并不是很有趣.

@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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