struct mm_struct {

     struct vm_area_struct * mmap;    //指向虚拟区间(VMA)的链表

     struct rb_root mm_rb;            //指向线性区对象红黑树的根

     struct vm_area_struct * mmap_cache;     //指向最近找到的虚拟区间

     unsigned long(*get_unmapped_area) (struct file *filp,

     unsigned long addr, unsigned long len,

     unsigned long pgoff, unsigned long flags);//在进程地址空间中搜索有效线性地址区

     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);//释放线性地址区间时调用的方法

     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;          //内核从这个地址开始搜索进程地址空间中线性地址的空闲区域

     pgd_t * pgd;                            //指向页全局目录

     atomic_t mm_users;                      //次使用计数器，使用这块空间的个数

     atomic_t mm_count;                      //主使用计数器

     int map_count;                          //线性的个数

     struct rw_semaphore mmap_sem;           //线性区的读/写信号量

     spinlock_t page_table_lock;             //线性区的自旋锁和页表的自旋锁

     struct list_head mmlist;              //指向内存描述符链表中的相邻元素

     /* 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代表的类型实际是typedef atomic_long_t

     mm_counter_t _anon_rss;

     mm_counter_t _swap_usage;

     unsigned long hiwater_rss;    //进程所拥有的最大页框数

     unsigned long hiwater_vm;     //进程线性区中最大页数

     unsigned long total_vm, locked_vm, shared_vm, exec_vm;

     //total_vm 进程地址空间的大小(页数）

     //locked_vm 锁住而不能换出的页的个数

     //shared_vm 共享文件内存映射中的页数

     unsigned long stack_vm, reserved_vm, def_flags, nr_ptes;

     //stack_vm 用户堆栈中的页数

     //reserved_vm 在保留区中的页数或者在特殊线性区中的页数

     //def_flags 线性区默认的访问标志

     //nr_ptes 进程的页表数

     unsigned long start_code, end_code, start_data, end_data;

     //start_code 可执行代码的起始地址

     //end_code 可执行代码的最后地址

     //start_data已初始化数据的起始地址

     // end_data已初始化数据的最后地址

     unsigned long start_brk, brk, start_stack;

     //start_stack堆的起始位置

     //brk堆的当前的最后地址

     //用户堆栈的起始地址

     unsigned long arg_start, arg_end, env_start, env_end;

     //arg_start 命令行参数的起始地址

     //arg_end命令行参数的起始地址

     //env_start环境变量的起始地址

     //env_end环境变量的最后地址

     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交换的位掩码

     /* Architecture-specific MM context */

     mm_context_t context; //指向有关特定结构体系信息的表

     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;  //用于保护异步I/O上下文链表的锁

     struct hlist_head       ioctx_list;//异步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[];

 #else

     //有多少任务分享这个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

 };