Linux內存描述符mm_struct初窺

上次講了Linux進程描述符（http://www.linuxidc.com/Linux/2012-02/53702.htm），這次我們在講講內存描述符，Linux的內存描述符也用一個結構體來表示，具體是mm_struct結構體，在linux/mm_types.h裡定義。Linux操作系統就是用這個結構體實現內存的管理，我們先看一下具體的字段情況。

1. struct mm_struct {
2. //擁有該結構體的進程的虛擬地址空間的大小
3. unsigned long task_size;
4. /* if non-zero, the largest hole below free_area_cache */
5. unsigned long cached_hole_size;
7. /* first hole of size cached_hole_size or larger */
8. unsigned long free_area_cache;
10. //在用戶空間下有多少用戶使用該內存
12. atomic_t mm_users; /* How many users with user space? */
14. //該結構體的引用計數值
15. atomic_t mm_count;
18. /*又出現了list_head,詳情請參考，簡單來講，list_head和list_for_each、list_entry共同實現了其“包含體”的鏈表。*/
20. struct list_head mmlist;
23. /*以下是關於代碼段、數據段，棧、環境變量、參數的起始地址或結束地址等*/
24. unsigned long total_vm, locked_vm, shared_vm, exec_vm;
25. unsigned long stack_vm, reserved_vm, def_flags, nr_ptes;
26. unsigned long start_code, end_code, start_data, end_data;
27. unsigned long start_brk, brk, start_stack;
28. unsigned long arg_start, arg_end, env_start, env_end;
29. /*
30. * Last value of global fault stamp as seen by this process.
31. * In other words, this value gives an indication of how long
32. * it has been since this task got the token.
33. * Look at mm/thrash.c
34. */
35. unsigned int faultstamp;
36. unsigned int token_priority;
37. unsigned int last_interval;
39. };

該結構體可以通過進程描述符來得到，比如current是當前進程的描述符，則current->mm是指向內存的指針。mm是指向struct mm_struct的指針。若還想對Linux的進程描述符有一定了解，可以參考task_struct。見 http://www.linuxidc.com/Linux/2012-02/53702.htm