Linux内存空间按地址,linux内存映射/内存区域/地址空间的概念

内存区域的结构函数：vm_area_struct,通常称为VMA，是指虚拟内存，在include/linux/mm_types.h定义

书上常说的内存区块，指的就是内存映射后的虚拟地址区块，内存映射如下面所述，是指从物理内存映射到虚拟内存

struct vm_area_struct {

struct mm_struct * vm_mm;/* The address space we belong to. */

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;

pgprot_t vm_page_prot;/* Access permissions of this VMA. */

unsigned long vm_flags;/* Flags, see mm.h. */

struct rb_node vm_rb;

/*

* For areas with an address space and backing store,

* linkage into the address_space->i_mmap prio tree, or

* linkage to the list of like vmas hanging off its node, or

* linkage of vma in the address_space->i_mmap_nonlinear list.

*/

union {

struct {

struct list_head list;

void *parent;/* aligns with prio_tree_node parent */

struct vm_area_struct *head;

} vm_set;

struct raw_prio_tree_node prio_tree_node;

} 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, *not* PAGE_CACHE_SIZE */

struct file * vm_file;/* File we map to (can be NULL). */

void * vm_private_data;/* was vm_pte (shared mem) */

unsigned long vm_truncate_count;/* truncate_count or restart_addr */

#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

};

内存描述符结构函数：mm_struct。在include/linux/mm_types.h

struct mm_struct {

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

struct rb_root mm_rb;

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

#ifdef CONFIG_MMU

unsigned long (*get_unmapped_area) (struct file *filp,

unsigned long addr, unsigned long len,

unsigned long pgoff, unsigned long flags);

void (*unmap_area) (struct mm_struct *mm, unsigned long addr);

#endif

unsigned long mmap_base;/* base of mmap area */

unsigned long task_size;/* size of task vm space */

unsigned long cached_hole_size; /* if non-zero, the largest hole below free_area_cache */

unsigned long free_area_cache;/* first hole of size cached_hole_size or larger */

pgd_t * pgd;

atomic_t mm_users;/* How many users with user space? */

atomic_t mm_count;/* How many references to "struct mm_struct" (users count as 1) */

int map_count;/* number of VMAs */

struct rw_semaphore mmap_sem;

spinlock_t page_table_lock;/* Protects page tables and some counters */

struct list_head mmlist;/* List of maybe swapped mm's.These are globally strung

* together off init_mm.mmlist, and are protected

* by mmlist_lock

*/

unsigned long hiwater_rss;/* High-watermark of RSS usage */

unsigned long hiwater_vm;/* High-water virtual memory usage */

unsigned long total_vm, locked_vm, shared_vm, exec_vm;

unsigned long stack_vm, reserved_vm, def_flags, nr_ptes;

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 saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */

/*

* Special counters, in some configurations protected by the

* page_table_lock, in other configurations by being atomic.

*/

struct mm_rss_stat rss_stat;

struct linux_binfmt *binfmt;

cpumask_t cpu_vm_mask;

/* Architecture-specific MM context */

mm_context_t context;

/* Swap token stuff */

/*

* Last value of global fault stamp as seen by this process.

* In other words, this value gives an indication of how long

* it has been since this task got the token.

* Look at mm/thrash.c

*/

unsigned int faultstamp;

unsigned int token_priority;

unsigned int last_interval;

unsigned long flags; /* Must use atomic bitops to access the bits */

struct core_state *core_state; /* coredumping support */

#ifdef CONFIG_AIO

spinlock_tioctx_lock;

struct hlist_headioctx_list;

#endif

#ifdef CONFIG_MM_OWNER

/*

* "owner" points to a task that is regarded as the canonical

* user/owner of this mm. All of the following must be true in

* order for it to be changed:

*

* current == mm->owner

* current->mm != mm

* new_owner->mm == mm

* new_owner->alloc_lock is held

*/

struct task_struct *owner;

#endif

#ifdef CONFIG_PROC_FS

/* store ref to file /proc//exe symlink points to */

struct file *exe_file;

unsigned long num_exe_file_vmas;

#endif

#ifdef CONFIG_MMU_NOTIFIER

struct mmu_notifier_mm *mmu_notifier_mm;

#endif

};

以下参考http://blog.csdn.net/hongchangfirst/article/details/7076207

该结构体可以通过进程描述符来得到，比如current是当前进程的描述符，则current->mm是指向内存的指针。mm是指向struct mm_struct的指针。

若还想对Linux的进程描述符有一定了解，可以参考task_struct。

内存映射是要把硬件映射到虚拟内存，例如一个硬件设备，把它映射到虚拟内存/dev下面，然后访问。一开始我的疑问是它是虚拟内存映射到物理内存，还是反过来？这样看来，应该是物理内存映射到虚拟内存。