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; |
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