读核日记(八) --linux的内存管理机制(2)

地址的映射机制

地址的映射机制,主要完成主存.辅存.和虚存之间的关联.包括磁盘文件到虚存的映射和虚存与内存的映射关系.为了虚拟存储和进程调度相一致.linux 采用可一系列的数据结构,和一个硬件缓存(TLB)来实现地址映射机制.

mm_strut 用来描述进程的缓存.

struct mm_struct

{

struct vm_area_struct * mmap; /* list of VMAs */

struct vm_area_struct * mmap_avl; /* tree of VMAs */

struct vm_area_struct * mmap_cache; /* last find_vma result */

pgd_t * pgd;

atomic_t count;

int map_count; /* number of VMAs */

struct semaphore mmap_sem;

spinlock_t page_table_lock;

unsigned long context;

unsigned long start_code, end_code, start_data, end_data;

unsigned long start_brk, brk, start_stack;

unsigned long arg_start, arg_end, env_start, env_end;

unsigned long rss, total_vm, locked_vm;

unsigned long def_flags;

unsigned long cpu_vm_mask;

unsigned long swap_cnt; /* number of pages to swap on next pass */

unsigned long swap_address;

/*

* This is an architecture-specific pointer: the portable

* part of Linux does not know about any segments.

*/

void * segments;

};

他描述了一个进程的页目录,有关进程的上下文信息.以及数据.代码.堆栈的启示结束地址.还有虚拟存储取得数目.以及调度存储用的链表指针.他的参差比较高

较高层次的vm_area-struct 是描述进程的虚拟地址区域.他形成一个算相链表.按虚地址下降排列.这样当内核需要在一个给定进程页上执行给定操作时.客从双向列表中找到该项.在世想有关页的处理.如.页错误.页换出等等

他的具体结构如下:

struct vm_area_struct {

struct mm_struct * vm_mm; /* VM area parameters */

unsigned long vm_start;

unsigned long vm_end;

/* linked list of VM areas per task, sorted by address */

struct vm_area_struct *vm_next;

pgprot_t vm_page_prot;

unsigned short vm_flags;

/* AVL tree of VM areas per task, sorted by address */

short vm_avl_height;

struct vm_area_struct * vm_avl_left;

struct vm_area_struct * vm_avl_right;

/* For areas with inode, the list inode-i_mmap, for shm areas,

* the list of attaches, otherwise unused.

*/

struct vm_area_struct *vm_next_share;

struct vm_area_struct **vm_pprev_share;

struct vm_operations_struct * vm_ops;

unsigned long vm_offset;

struct file * vm_file;

unsigned long vm_pte; /* shared mem */

};

而page 结构 则是对物理页进行描述的一个数据结构,他不是一个真正的物理页.而只不过是描述了一个物理页的内容和框架.作了逻辑页的一个标志;.他的标志域定义了这个页在进行的操作.链域则定义了一个双项链表.时的页框.可以很容易的查找到.为实际物理内存的使用直到方便

他的具体结构如下

typedef struct page {

/* these must be first (free area handling) */

struct page *next;

struct page *prev;

struct inode *inode;

unsigned long offset;

struct page *next_hash;

atomic_t count;

unsigned long flags; /* atomic flags, some possibly updated asynchronously */

wait_queue_head_t wai