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  "contentMarkdown": "# 【内存】内存底层深入\n> 创建时间：2021/7/2 12:59\n\n## 【内存】内存底层深入\n\n  * 【内存】内存底层深入\n    * 基本知识\n      * 物理内存的访问\n      * 台式设备和移动设备内存架构差异\n    * 内存分页\n    * Unity\n    * Ref\n\n## 基本知识\n\n### 物理内存的访问\n\nCPU访问内存是一个慢速过程。\n访问过程：先访问Cache，Cache包含L1，L2，L3，也就是一级缓存，二级缓存和三级缓存，若在这些缓存里全没找到我们要的数据，再去访问内存，接着会把找到的数据存放到Cache中，完成一次操作。\n\n过多的Cache Miss就会导致大量的内存和Cache的IO交换，浪费大量时间。\n\n> Unity ECS方案: 可以将存储在内存中的不连续数据，变为连续的数据，从而降低Cache Miss的概率。\n\n### 台式设备和移动设备内存架构差异\n\n  * 移动设备 **没有独立显卡** 。\n\n  * 移动设备 **没有独立显存** ，内存和显存是同一块内存。\n\n> 所以有可能我们游戏占用的内存并不大，但是依旧爆内存了，其实是因为显存分配不出来了。这种情况，我们可以去查看一下Log，例如Android会有一个 OpenGL Error：Out Of Memory。\n\n  * 移动设备的CPU面积更小，因此会导致 **缓存级数更少** ，大小也更小，例如一般的台式机三级缓存可能有8-16M，而移动设备则只有2M左右。\n\n## 内存分页\n\n内存分页（IOS上大部分为16K/page）是内存管理的最小单位，当Unity需要申请内存的时候，都会以block的方式（若干个页）进行申请。如果某一页在若干次GC（IOS为8次）之后仍然为Empty的话，它就会被释放，实际的物理内存就会被还给物理内存。\n\n## Unity\n\n## Ref\n\n<https://zhuanlan.zhihu.com/p/370467923>\n<https://zhuanlan.zhihu.com/p/362941227>\n"
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