Linux 内核 内存管理内存映射相关数据结构 ③ ( vm_area_struct 结构体成员分析 | shared 成员 | anon_vma_chain 成员 | anon_vma 成员 )

Posted 2022-04-15 韩曙亮

文章目录

• 一、vm_area_struct 结构体成员分析
• • 1、shared 成员
  • 2、anon_vma_chain 成员
  • 3、anon_vma 成员
• 二、vm_area_struct 结构体完整源码

在博客 【Linux 内核 内存管理】虚拟地址空间布局架构 ⑦ ( vm_area_struct 结构体成员分析 | vm_start | vm_end | vm_next | vm_prev |vm_rb) 中 , 分析了 vm_start vm_end vm_next vm_prev vm_rb 这 $5$ 个结构体成员作用 ;

在博客 【Linux 内核 内存管理】内存映射相关数据结构 ② ( vm_area_struct 结构体成员分析 | vm_mm 成员 | vm_page_prot 成员 | vm_flags 成员 ) 中 , 分析了 vm_area_struct 结构体中的 vm_mm vm_page_prot vm_flags 成员作用 ;

一、vm_area_struct 结构体成员分析

---

1、shared 成员

在 内存映射 中的 " 文件映射 " 中 , 将 " 文件 " 映射到 " 用户虚拟地址空间 " 后 , 需要将该文件的 地址空间结构 address_space 的成员 i_mmap 指针指向的 " 区域树 " 加入到该 shared 结构体中 ;

shared 成员中 , 可以查询 文件 的 哪些 " 文件区间的数据 " , 被映射到了 哪些 " 虚拟内存区域 " 中 ;

	/*
	 * For areas with an address space and backing store,
	 * linkage into the address_space->i_mmap interval tree.
	 */
	struct 
		struct rb_node rb;
		unsigned long rb_subtree_last;
	 shared;

2、anon_vma_chain 成员

" 虚拟内存区域 “ vm_area_struct 结构体实例 所 ” 关联 " 的 anon_vma 实例 ,

会与 " 父进程 " 的 anon_vma 实例 串联起来 , 组成一个 链表 ;

struct list_head anon_vma_chain 成员 就是该 anon_vma 实例 组成的 链表 ;

	/*
	 * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma
	 * list, after a COW of one of the file pages.	A MAP_SHARED vma
	 * can only be in the i_mmap tree.  An anonymous MAP_PRIVATE, stack
	 * or brk vma (with NULL file) can only be in an anon_vma list.
	 */
	struct list_head anon_vma_chain; /* Serialized by mmap_sem &
					  * page_table_lock */

3、anon_vma 成员

anon_vma 结构体 用于 组织 " 匿名内存页 " 被 映射到的 " 用户虚拟地址空间 " ,

anon_vma 成员指向了 anon_vma 结构体实例 ;

	struct anon_vma *anon_vma;	/* Serialized by page_table_lock */

二、vm_area_struct 结构体完整源码

---

vm_area_struct 结构体完整源码 :

/*
 * This struct defines a memory VMM memory area. There is one of these
 * per VM-area/task.  A VM area is any part of the process virtual memory
 * space that has a special rule for the page-fault handlers (ie a shared
 * library, the executable area etc).
 */
struct vm_area_struct 
	/* The first cache line has the info for VMA tree walking. */

	unsigned long vm_start;		/* Our start address within vm_mm. */
	unsigned long vm_end;		/* The first byte after our end address
					   within vm_mm. */

	/* linked list of VM areas per task, sorted by address */
	struct vm_area_struct *vm_next, *vm_prev;

	struct rb_node vm_rb;

	/*
	 * Largest free memory gap in bytes to the left of this VMA.
	 * Either between this VMA and vma->vm_prev, or between one of the
	 * VMAs below us in the VMA rbtree and its ->vm_prev. This helps
	 * get_unmapped_area find a free area of the right size.
	 */
	unsigned long rb_subtree_gap;

	/* Second cache line starts here. */

	struct mm_struct *vm_mm;	/* The address space we belong to. */
	pgprot_t vm_page_prot;		/* Access permissions of this VMA. */
	unsigned long vm_flags;		/* Flags, see mm.h. */

	/*
	 * For areas with an address space and backing store,
	 * linkage into the address_space->i_mmap interval tree.
	 */
	struct 
		struct rb_node rb;
		unsigned long rb_subtree_last;
	 shared;

	/*
	 * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma
	 * list, after a COW of one of the file pages.	A MAP_SHARED vma
	 * can only be in the i_mmap tree.  An anonymous MAP_PRIVATE, stack
	 * or brk vma (with NULL file) can only be in an anon_vma list.
	 */
	struct list_head anon_vma_chain; /* Serialized by mmap_sem &
					  * page_table_lock */
	struct anon_vma *anon_vma;	/* Serialized by page_table_lock */

	/* Function pointers to deal with this struct. */
	const struct vm_operations_struct *vm_ops;

	/* Information about our backing store: */
	unsigned long vm_pgoff;		/* Offset (within vm_file) in PAGE_SIZE
					   units */
	struct file * vm_file;		/* File we map to (can be NULL). */
	void * vm_private_data;		/* was vm_pte (shared mem) */

#ifndef CONFIG_MMU
	struct vm_region *vm_region;	/* NOMMU mapping region */
#endif
#ifdef CONFIG_NUMA
	struct mempolicy *vm_policy;	/* NUMA policy for the VMA */
#endif
	struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
;