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FIX: 修正 32 位系统单级页表大小的计算逻辑与单位换算 #2765

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Snailclimb merged 1 commit into from
Dec 18, 2025
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FIX: 修正 32 位系统单级页表大小的计算逻辑与单位换算 #2765

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2 changes: 1 addition & 1 deletion docs/cs-basics/operating-system/operating-system-basic-questions-02.md
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Expand Up @@ -211,7 +211,7 @@ MMU 将虚拟地址翻译为物理地址的主要机制有 3 种:

#### 单级页表有什么问题？为什么需要多级页表？

以 32 位的环境为例，虚拟地址空间范围共有 2^32（4G）。假设 一个页的大小是 2^12（4KB），那页表项共有 4G / 4K = 2^20 个。每个页表项为一个地址，占用 4 字节，`2^20 * 2^2 / 1024 * 1024= 4MB`。也就是说一个程序啥都不干，页表大小就得占用 4M。
以 32 位的环境为例，虚拟地址空间范围共有 2^32（4G）。假设 一个页的大小是 2^12（4KB），那页表项共有 4G / 4K = 2^20 个。每个页表项为一个地址，占用 4 字节，`(2^20 * 2^2) / (1024 * 1024)= 4MB`。也就是说一个程序啥都不干，页表大小就得占用 4M。

系统运行的应用程序多起来的话，页表的开销还是非常大的。而且，绝大部分应用程序可能只能用到页表中的几项，其他的白白浪费了。

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