linux将虚拟地址转物理地址的过程探索[页表]

最新推荐文章于 2025-05-26 22:11:19 发布

wangshankun2011

最新推荐文章于 2025-05-26 22:11:19 发布

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分类专栏：家庭路由器文章标签： linux 内存物理地址

本文链接：https://blog.youkuaiyun.com/wangshankun2011/article/details/46279331

本文探讨了Linux内存管理中的页表机制，解释了如何将虚拟地址转换为物理地址。通过分析内存模型，了解到每个4KB的页对应一个页框编号(PFN)。介绍了使用CONFIG_PROC_PAGE_MONITOR内核选项，以及page-collect和pagemap.c等工具来查看和解析页表信息，从而获取进程中的变量物理地址。

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先是原理简单的介绍下：

Linux把物理内存分为了固定统一大小的块，称为page[页]，一般为4KB，并且每个页都有一个编号 [page frame number]。
这样一个512M大小的内存将包括128K个页。page table的作用就是将进程操作的地址[虚拟地址]转换成物理地址。

Linux Memory Model
==================
----------------------------------------------


       process 1
      +----------+     page table     +--------+     page table
      |          |    +--------+  +-->| PFN 3  |     +--------+
      +----------+    |--------|  |   +--------+     |--------|
      | VPFN 100 |--->|--------|  |   | PFN 2  |     |--------|
      +----------+    |  ...   |--+   +--------+     |--------|
      |   ...    |    +--------+      | PFN 1  |<----|   ...  |<--+
      +----------+                    +--------+     +--------+   |
                                      | PFN 0  |                  |
                                      +--------+              process 2  
                                                             +---------+
                                                             |         |
                                                             +---------+

Physical memory is broken into fix-sized pages, each page is assigned a
number, known as Page Frame Number (PFN). Corresponding to the physical pages,
process address space can also be broken into pages, known as virtual pages.
And which virtual pages are actually loaded into physical frames is the job of
VM demand paging algorithm.



The virtual memory address is composed of two parts:

    0-11 bit is page offset
    12-31 is virtual page frame number (VPFN)

VPFN is the index into page table, if such page entry has a valid flag, then
processor take its page table entry and get physical page frame number,
multiply by its page size to get the page's base address. Add offset to this
base address, you get the physical address you are looking for.