docs: add linux-mm-4.md #307
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Plucky923
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Nov 24, 2025
| swap机制和演进 | ||
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| 在深入探索内核 Swap 机制的奥秘之前，我们必须首先明确其存在的根基——物理内存管理。系统的所有活动都围绕着对物理页面（在现代内核中更常被称为 page/folio）的分配与使用。这些以 4KB 为基本单位的物理内存页，在系统上电初始化后，便由内核的伙伴系统（Buddy System）统一管理，等待着为进程和内核自身提供服务。 |
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一个物理页面应该是一个page，folio是另外一种抽象，所以这里的描述并不是很严谨
| 为了挣脱“巨锁”的束缚，内核开发者们迈出了演进的第一步。他们借用了文件系统页面缓存（Page Cache）的管理框架，将庞大的交换空间逻辑上切分为以 64MB 为单位的管理单元，即 swap_address_space。 | ||
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| 每一个 64MB 的 address_space 都由一棵独立的 XArray 树 来管理。这成功地将一把“全局锁”打碎成了多把“64MB 区域锁”，显著缓解了锁竞争（注：关于 XArray 的精妙设计，强烈推荐阅读 Kairui 哥的深度解析文章） | ||
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新增swap机制介绍，这部分和之前的内存讲解有一定联系，本身是内存管理的一部分但是不是之前内容的后续部分，此次贡献为swap 机制的原理和一些新的改进部分，后续围绕改进和涉及的数据结构会做贡献，具体以后续讨论结果增加，新增部分格式对齐了前面的章节