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PUB:20151123 Data Structures in the Linux Kernel

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translated/tech/20151123 Data Structures in the Linux Kernel.md → published/20151123 Data Structures in the Linux Kernel.md
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@ -1,4 +1,4 @@
Linux内核中的数据结构 —— 基数树
Linux 内核里的数据结构 —— 基数树
================================================================================
基数树 Radix tree
@ -11,35 +11,35 @@ Linux内核中的数据结构 —— 基数树
让我们先说说什么是 `基数树` 吧。基数树是一种 `压缩的字典树 (compressed trie)` ，而[字典树](http://en.wikipedia.org/wiki/Trie)是实现了关联数组接口并允许以 `键值对` 方式存储值的一种数据结构。这里的键通常是字符串，但可以使用任意数据类型。字典树因为它的节点而与 `n叉树` 不同。字典树的节点不存储键，而是存储单个字符的标签。与一个给定节点关联的键可以通过从根遍历到该节点获得。举个例子：
```
               +-----------+
               |           |
               |    " "    |
+-----------+
| |
        +------+-----------+------+
        |                         |
        |                         |
   +----v------+            +-----v-----+
   |           |            |           |
   |    g      |            |     c     |
| " " |
| |
+------+-----------+------+
| |
| |
+----v------+ +-----v-----+
| | | |
   +-----------+            +-----------+
        |                         |
        |                         |
   +----v------+            +-----v-----+
   |           |            |           |
   |    o      |            |     a     |
| g | | c |
| | | |
   +-----------+            +-----------+
                                  |
                                  |
                            +-----v-----+
                            |           |
                            |     t     |
+-----------+ +-----------+
| |
| |
+----v------+ +-----v-----+
| | | |
| o | | a |
| | | |
+-----------+ +-----------+
|
|
+-----v-----+
| |
                            +-----------+
| t |
| |
+-----------+
```
因此在这个例子中，我们可以看到一个有着两个键 `go` 和 `cat` 的 `字典树` 。压缩的字典树或者说 `基数树` ，它和 `字典树` 的不同之处在于，所有只有一个孩子的中间节点都被删除。
因此在这个例子中，我们可以看到一个有着两个键 `go` 和 `cat` 的 `字典树` 。压缩的字典树也叫做 `基数树` ，它和 `字典树` 的不同之处在于，所有只有一个子节点的中间节点都被删除。
Linux 内核中的基数树是把值映射到整形键的一种数据结构。[include/linux/radix-tree.h](https://github.com/torvalds/linux/blob/master/include/linux/radix-tree.h)文件中的以下结构体描述了基数树：
@ -86,10 +86,10 @@ struct radix_tree_node {
unsigned long tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
};
```
这个结构体包含的信息有父节点中的偏移以及到底端(叶节点)的高度、孩子节点的个数以及用于访问和释放节点的字段成员。这些字段成员描述如下：
这个结构体包含的信息有父节点中的偏移以及到底端(叶节点)的高度、子节点的个数以及用于访问和释放节点的字段成员。这些字段成员描述如下：
* `path` - 父节点中的偏移和到底端(叶节点)的高度
* `count` - 孩子节点的个数;
* `count` - 子节点的个数;
* `parent` - 父节点指针;
* `private_data` - 由树的用户使用;
* `rcu_head` - 用于释放节点;
@ -188,9 +188,9 @@ unsigned int radix_tree_gang_lookup(struct radix_tree_root *root,
--------------------------------------------------------------------------------
via: https://github.com/0xAX/linux-insides/edit/master/DataStructures/radix-tree.md
via: https://github.com/0xAX/linux-insides/blob/master/DataStructures/radix-tree.md
作者：[0xAX]
作者：0xAX
译者：[cposture](https://github.com/cposture)
校对：[Mr小眼儿](https://github.com/tinyeyeser)