内核如何管理你的内存.docx

 HYPERLINK "/gustavo/blog/post/how-the-kernel-manages-your-memory" How The Kernel Manages Your Memory 内核如何管理你的内存 After examining the? HYPERLINK "/gustavo/blog/post/anatomy-of-a-program-in-memory" virtual address layout?of a process, we turn to the kernel and its mechanisms for managing user memory. Here is gonzo again: 在上一篇关于一个进程的虚拟地址布局之后，是时候来看看内核和它管理用户内存的机制了。下面还是以上一篇提到到的gonzo为例： Linux processes are implemented in the kernel as instances of? HYPERLINK "http://lxr.linux.no/linux+v/include/linux/sched.h" \l "L1075" task_struct, the process descriptor. The? HYPERLINK "http://lxr.linux.no/linux+v/include/linux/sched.h" \l "L1129" mm?field in task_struct points to the?memory descriptor,? HYPERLINK "http://lxr.linux.no/linux+v/include/linux/mm_types.h" \l "L173" mm_struct, which is an executive summary of a program’s memory. It stores the start and end of memory segments as shown above, the? HYPERLINK "http://lxr.linux.no/linux+v/include/linux/mm_types.h" \l "L197" number?of physical memory pages used by the process (rss?stands for Resident Set Size), the HYPERLINK "http://lxr.linux.no/linux+v/include/linux/mm_types.h" \l "L206" ?amount?of virtual address space used, and other tidbits. Within the memory descriptor we also find the two work horses for managing program memory: the set of?virtual memory areas?and thepage tables. Gonzo’s memory areas are shown below: Linux的进程在kernel中是由task_struct来实现的。其中有一个mm域指向这个进程所使用的内存的描述符，mm_struct。它包含了如上所示的各个段的开始和结束的地址（使用的是unsigned long类型来表示），被这个进程所使用的物理内存页的个数，各种被使用到的虚拟地址空间（total_vm, shared_vm,...）和其它一些内容。从这个结构体中我们能看到两块主要的用来管理程序内存的成员：虚拟内存空间（vm_area_struct）和页表（pgd,这是一个平台相关的结构）。下图是Gonzo的虚拟内存的布局。 Each virtual memory area (VMA) is a contiguous range of virtual addresses; these areas never overlap. An instance of? HYPERLINK "http://lxr.linux.no/linux+v/include/linux/mm_types.h" \l "L99" vm_area_struct?fully describes a memory area, including its start and end addresses,? HYPERLINK "http://lxr.linux.no/linux+v2.6.28/inc