为了理解反向映射技术，让我们来首先简单了解Linux虚拟内存系统的一些基本原理。

To understand the reverse mapping technique, let's quickly go through some fundamentals of the Linux virtual memory system.

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一个虚拟内存系统的全部重点就是：你可以拥有一个虚拟的地址空间，它比计算机上的物理内存总量还要大。

The whole point of a virtual memory system is that you can have a virtual address space that's much bigger than the amount of physical memory on the computer.

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尽管如此，rmap的性能——尤其是处于高负载的高端系统——相对于2.4内核的虚拟内存系统还是有了显著的提高。

Despite this, the performance of the rmap patch — especially on high-end systems and under heavy loads — is significantly better than the 2.4 kernel's VM system.

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