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fix:修复了语句错误 #339

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fix:修复了语句错误 #339

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2 changes: 1 addition & 1 deletion os/6_file_system/file_system.md
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Expand Up @@ -403,7 +403,7 @@ Linux 系统的 ext 文件系统就是采用了哈希表，来保存目录的内

我们都知道磁盘 I/O 是非常慢的，所以 Linux 内核为了减少磁盘 I/O 次数，在系统调用后，会把用户数据拷贝到内核中缓存起来，这个内核缓存空间也就是「页缓存」，只有当缓存满足某些条件的时候，才发起磁盘 I/O 的请求。

那么，**根据是「否利用操作系统的缓存」，可以把文件 I/O 分为直接 I/O 与非直接 I/O**：
那么，**根据「是否利用操作系统的缓存」，可以把文件 I/O 分为直接 I/O 与非直接 I/O**：

- 直接 I/O，不会发生内核缓存和用户程序之间数据复制，而是直接经过文件系统访问磁盘。
- 非直接 I/O，读操作时，数据从内核缓存中拷贝给用户程序，写操作时，数据从用户程序拷贝给内核缓存，再由内核决定什么时候写入数据到磁盘。
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