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Understanding the Linux Kernel, 3rd Edition by Marco Cesati, Daniel P. Bovet

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The Memory Descriptor

All information related to the process address space is included in an object called the memory descriptor of type mm_struct. This object is referenced by the mm field of the process descriptor. The fields of a memory descriptor are listed in Table 9-2.

Table 9-2. The fields of the memory descriptor

Type

Field

Description

struct

vm_area_struct *

mmap

Pointer to the head of the list of memory region objects

struct rb_root

mm_rb

Pointer to the root of the red-black tree of memory region objects

struct

vm_area_struct *

mmap_cache

Pointer to the last referenced memory region object

unsigned long (*)( )

get_unmapped_area

Method that searches an available linear address interval in the process address space

void (*)( )

unmap_area

Method invoked when releasing a linear address interval

unsigned long

mmap_base

Identifies the linear address of the first allocated anonymous memory region or file memory mapping (see the section "Program Segments and Process Memory Regions" in Chapter 20)

unsigned long

free_area_cache

Address from which the kernel will look for a free interval of linear addresses in the process address space

pgd_t *

pgd

Pointer to the Page Global Directory

atomic_t

mm_users

Secondary usage counter

atomic_t

mm_count

Main usage counter

int

map_count

Number of memory regions

struct

rw_semaphore

mmap_sem

Memory regions' read/write semaphore

spinlock_t

page_table_lock

Memory regions' and Page Tables' spin lock

struct list_head

mmlist

Pointers ...

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