Linux之内存管理mm_struct

比眉伴天荒 2022-06-17 03:23 166阅读 0赞

每个进程都有自己的mm\_struct，使得每个进程都有自己独立的虚拟的地址空间  
在每个进程的task\_struct里都会有一个struct mm\_struct\*指向每个进程自己的mm\_struct，mm\_sruct是内存描述符，在每个mm\_struct又都有一个pgd\_t \* 使其指向页表，然后通过页表实现从虚拟地址到物理地址的映射。

Linux虚拟地址用户空间分布  
![这里写图片描述][SouthEast]

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[2];
    #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
    };

![这里写图片描述][SouthEast 1]

[SouthEast]: /images/20220617/acae912201184e40a6e991a0c2020d26.png
[SouthEast 1]: /images/20220617/f6d2fbddae9642768dd8b7c98a99150b.png