共享页

2020.8.6

详细：直系进程因为可以共享fd，所以mmap的标志位MAP_SHARED应该可以很简单的共享页（若是MAP_PRIVATE标志位，就是各个linux教程里常常提到的fork时copy-on-write的页）。但是非直系进程怎么处理？

2020.8.9

参考这篇问答Process VS thread : can two processes share the same shared memory ? can two threads ?中Gray的回答，

If a process has not been forked from another then they typically do not share any memory. One exception is if you are running two instances of the same program then they may share code and maybe even static data segments but no other pages will be shared.

即非直系进程间不会有共享的内存，有的话大概是代码段和静态数据段（大概是由ELF的加载器判断然后完成的？）

参考linux提供的系统调用

  • shmget: Creating Shared Memory
  • shmat: Attaching to Shared Memory
  • shmdt: Dettaching to Shared Memory
  • shmctl: Shared Meory Control

哪些操作会影响/proc/[pid]/maps

2020.8.10

参考man proc有关/proc/[pid]/maps的说明，系统调用mmap（当然也有munmap）添加和删除maps项，系统调用ptrace管理访问maps的权限。