Understanding the Linux Kernel, Second Edition

Memory Regions

Linux implements a memory region by means of an object of type vm_area_struct; its fields are shown in Table 8-3.

Table 8-3. The fields of the memory region object

Type	Field	Description
struct mm_struct *	vm_mm	Pointer to the memory descriptor that owns the region
unsigned long	vm_start	First linear address inside the region
unsigned long	vm_end	First linear address after the region
struct vm_area_struct *	vm_next	Next region in the process list
pgprot_t	vm_page_prot	Access permissions for the page frames of the region
unsigned long	vm_flags	Flags of the region
rb_node_t	vm_rb	Data for the red-black tree (see later in this chapter)
struct vm_area_struct *	vm_next_share	Pointer to the next element in the file memory mapping list
struct vm_area_struct **	vm_pprev_share	Pointer to previous element in the file memory mapping list
struct vm_operations_struct *	vm_ops	Pointer to the methods of the memory region
unsigned long	vm_pgoff	Offset in mapped file, if any (see Chapter 15)
struct file *	vm_file	Pointer to the file object of the mapped file, if any
unsigned long	vm_raend	End of current read-ahead window of the mapped file (see Section 15.2.4)
void *	vm_private_data	Pointer to private data of the memory region

Each memory region descriptor identifies a linear address interval. The vm_start field contains the first linear address of the interval, while the vm_end field ...