第二章 存儲管理 幾個重要的數據結構和函數

 

 

 

 

struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long addr)函數：

功能：給定一個屬於某個進程的虛擬地址，要求找到其所屬的區間以及相應的vma_area_struct結構；所找到的區間只要知足結束地址大於虛擬地址addr便可

參數：具體的哪一個進程mm_struct下；虛擬地址

流程：先驗證mm_struct中的mmap_cache（最近訪問區），若不符合再從AVL樹開始搜索，若沒有AVL樹則從mmap線性隊列開始

源碼：

 1: /* Look up the first VMA which satisfies addr < vm_end, NULL if none. */

 2: struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long addr)

 3: {

 4:     struct vm_area_struct *vma = NULL;

 5:  

 6:     if (mm) {

 7:         /* Check the cache first. */

 8:         /* (Cache hit rate is typically around 35%.) */

 9:         vma = mm->mmap_cache;//先從最近使用的vma_area_struct開始查找

 10:         if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {//若不在最近使用的vma_area_struct中，則從AVL樹或者線性隊列中搜索

 11:             if (!mm->mmap_avl) {

 12:                 /* Go through the linear list. */

 13:                 vma = mm->mmap;//線性隊列開始，此線性隊列是按照地址從低往高處排列的

 14:                 while (vma && vma->vm_end <= addr)

 15:                     vma = vma->vm_next;

 16:             } else {

 17:                 /* Then go through the AVL tree quickly. */

 18:                 struct vm_area_struct * tree = mm->mmap_avl;

 19:                 vma = NULL;

 20:                 for (;;) {

 21:                     if (tree == vm_avl_empty)

 22:                         break;

 23:                     if (tree->vm_end > addr) {

 24:                         vma = tree;

 25:                         if (tree->vm_start <= addr)

 26:                             break;

 27:                         tree = tree->vm_avl_left;

 28:                     } else

 29:                         tree = tree->vm_avl_right;

 30:                 }

 31:             }

 32:             if (vma)

 33:                 mm->mmap_cache = vma;//設置mm_struct中的mmap_cache爲最近訪問的虛擬區

 34:         }

 35:     }

 36:     return vma;

 37: }

 

void insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vmp)函數：

功能：將一個虛擬區間插入到一個進程mm_struct中去

參數：所要插入的mm_struct；虛擬區間

源碼：

 1: void insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vmp)

 2: {

 3:     lock_vma_mappings(vmp);

 4:     spin_lock(&current->mm->page_table_lock);

 5:     __insert_vm_struct(mm, vmp);

 6:     spin_unlock(&current->mm->page_table_lock);

 7:     unlock_vma_mappings(vmp);

 8: }

插入操做過程當中不容許收到任何干擾，加了兩把鎖。第一把表明新區間的vm_area_struct數據結構中，第二把表明着整個虛存空間mm_struct數據結構，不容許其它進程可以中途插進來。

 1: /* Insert vm structure into process list sorted by address

 2:  * and into the inode's i_mmap ring. If vm_file is non-NULL

 3:  * then the i_shared_lock must be held here.

 4:  */

 5: void __insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vmp)

 6: {

 7:     struct vm_area_struct **pprev;

 8:     struct file * file;

 9:  

 10:     if (!mm->mmap_avl) {//若沒有AVL樹，則將按地址從低往高選擇將新區間插入到線性隊列mm->mmap中去

 11:         pprev = &mm->mmap;

 12:         while (*pprev && (*pprev)->vm_start <= vmp->vm_start)

 13:             pprev = &(*pprev)->vm_next;

 14:     } else {//有AVL樹，則調整此區間在AVL樹中的位置，同時調整liner que

 15:         struct vm_area_struct *prev, *next;

 16:         avl_insert_neighbours(vmp, &mm->mmap_avl, &prev, &next);

 17:         pprev = (prev ? &prev->vm_next : &mm->mmap);

 18:         if (*pprev != next)

 19:             printk("insert_vm_struct: tree inconsistent with list\n");

 20:     }

 21:     vmp->vm_next = *pprev;

 22:     *pprev = vmp;

 23:  

 24:     mm->map_count++; //vvm個數加1

 25:     if (mm->map_count >= AVL_MIN_MAP_COUNT && !mm->mmap_avl)//對於一個mm_struct來講，只有vvm個數超過AVL_MIN_MAP_COUNT,纔會創建AVL樹

 26:         build_mmap_avl(mm);

 27:  

 28:     file = vmp->vm_file;

 29:     if (file) {//若此新區是與文件映射有關，則有相關處理：

 30:         struct inode * inode = file->f_dentry->d_inode;

 31:         struct address_space *mapping = inode->i_mapping;

 32:         struct vm_area_struct **head;

 33:  

 34:         if (vmp->vm_flags & VM_DENYWRITE)

 35:             atomic_dec(&inode->i_writecount);

 36:  

 37:         head = &mapping->i_mmap;

 38:         if (vmp->vm_flags & VM_SHARED)

 39:             head = &mapping->i_mmap_shared;

 40: 

 41:         /* insert vmp into inode's share list */

 42:         if((vmp->vm_next_share = *head) != NULL)

 43:             (*head)->vm_pprev_share = &vmp->vm_next_share;

 44:         *head = vmp;

 45:         vmp->vm_pprev_share = head;

 46:     }

 47: }