26     if (vma->vm_mm == NULL)  in vm_area_del()
38     if (vma->vm_prev == NULL && vma->vm_next == NULL) // 如果当前是剩余的最后一个vma  in vm_area_free()
39         vma->vm_mm->vmas = NULL;  in vm_area_free()
52     struct vm_area_struct *next = NULL;  in __vma_link_list()
67     if (next != NULL)  in __vma_link_list()
101     struct vm_area_struct *result = NULL;  in vma_find()
102     while (vma != NULL)  in vma_find()
154     if (prev == NULL) // 要将当前vma插入到链表的尾部  in vma_insert()
185     if (unlikely(anon_vma == NULL))  in __anon_vma_create_alloc()
186         return NULL;  in __anon_vma_create_alloc()
193     if (page != NULL)  in __anon_vma_create_alloc()
235     if (anon_vma->page != NULL)  in __anon_vma_free()
238         anon_vma->page->anon_vma = NULL;  in __anon_vma_free()
255     if (vma->anon_vma == NULL)  in __anon_vma_del()
273     vma->anon_vma = NULL;  in __anon_vma_del()