struct mm_struct {  struct vm_area_struct * mmap;  //指向虛擬區間(VMA)的鏈表  struct rb_root mm_rb;      //指向線性區對象紅黑樹的根  struct vm_area_struct * mmap_cache;   //指向最近找到的虛擬區間  unsigned long(*get_unmapped_area) (struct file *filp,  unsigned long addr, unsigned long len,  unsigned long pgoff, unsigned long flags);//在進程地址空間中搜索有效線性地址區  unsigned long(*get_unmapped_exec_area) (struct file *filp,    unsigned long addr, unsigned long len,    unsigned long pgoff, unsigned long flags);  void(*unmap_area) (struct mm_struct *mm, unsigned long addr);//釋放線性地址區間時調用的方法  unsigned long mmap_base;        /* base of mmap area */  unsigned long task_size;        /* size of task vm space */  unsigned long cached_hole_size;  unsigned long free_area_cache;     //內核從這個地址開始搜索進程地址空間中線性地址的空閑區域  pgd_t * pgd;              //指向頁全局目錄  atomic_t mm_users;           //次使用計數器，使用這塊空間的個數    atomic_t mm_count;           //主使用計數器  int map_count;             //線性的個數  struct rw_semaphore mmap_sem;      //線性區的讀/寫信號量  spinlock_t page_table_lock;       //線性區的自旋鎖和頁表的自旋鎖  struct list_head mmlist;       //指向內存描述符鏈表中的相鄰元素  /* Special counters, in some configurations protected by the  * page_table_lock, in other configurations by being atomic.  */  mm_counter_t _file_rss; //mm_counter_t代表的類型實際是typedef atomic_long_t  mm_counter_t _anon_rss;   mm_counter_t _swap_usage;  unsigned long hiwater_rss;  //進程所擁有的最大頁框數  unsigned long hiwater_vm;   //進程線性區中最大頁數  unsigned long total_vm, locked_vm, shared_vm, exec_vm;  //total_vm 進程地址空間的大小(頁數）  //locked_vm 鎖住而不能換出的頁的個數  //shared_vm 共享文件內存映射中的頁數  unsigned long stack_vm, reserved_vm, def_flags, nr_ptes;  //stack_vm 用戶堆棧中的頁數  //reserved_vm 在保留區中的頁數或者在特殊線性區中的頁數  //def_flags 線性區默認的訪問標志  //nr_ptes 進程的頁表數  unsigned long start_code, end_code, start_data, end_data;  //start_code 可執行代碼的起始地址  //end_code 可執行代碼的最后地址  //start_data已初始化數據的起始地址  // end_data已初始化數據的最后地址  unsigned long start_brk, brk, start_stack;  //start_stack堆的起始位置  //brk堆的當前的最后地址  //用戶堆棧的起始地址  unsigned long arg_start, arg_end, env_start, env_end;  //arg_start 命令行參數的起始地址  //arg_end命令行參數的起始地址  //env_start環境變量的起始地址  //env_end環境變量的最后地址  unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */  struct linux_binfmt *binfmt;  cpumask_t cpu_vm_mask; //用于惰性TLB交換的位掩碼  /* Architecture-specific MM context */  mm_context_t context; //指向有關特定結構體系信息的表  unsigned int faultstamp;  unsigned int token_priority;  unsigned int last_interval;  unsigned long flags; /* Must use atomic bitops to access the bits */  struct core_state *core_state; /* coredumping support */#ifdef CONFIG_AIO  spinlock_t       ioctx_lock; //用于保護異步I/O上下文鏈表的鎖  struct hlist_head    ioctx_list;//異步I/O上下文#endif#ifdef CONFIG_MM_OWNER  struct task_struct *owner;#endif#ifdef CONFIG_PROC_FS  unsigned long num_exe_file_vmas;#endif#ifdef CONFIG_MMU_NOTIFIER  struct mmu_notifier_mm *mmu_notifier_mm;#endif#ifdef CONFIG_TRANSPARENT_HUGEPAGE  pgtable_t pmd_huge_pte; /* protected by page_table_lock */#endif#ifdef __GENKSYMS__  unsigned long rh_reserved[2];#else  //有多少任務分享這個mm OOM_DISABLE  union {    unsigned long rh_reserved_aux;    atomic_t oom_disable_count;  };  /* base of lib map area (ASCII armour) */  unsigned long shlib_base;#endif};