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Understanding the Linux Kernel, Second 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 a data structure called a memory descriptor . This structure of type mm_struct is referenced by the mm field of the process descriptor. The fields of a memory descriptor are listed in Table 8-2.

Table 8-2. 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

rb_root_t

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

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 to adjacent elements in the list of memory descriptors

unsigned long

start_code

Initial address of executable code

unsigned long

end_code

Final address of executable code

unsigned long

start_data

Initial address of initialized data

unsigned long

end_data

Final address of initialized data

unsigned long

start_brk

Initial address of the heap

unsigned long

brk

Current final address of the heap

unsigned long

start_stack

Initial address ...

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