计算机系信息处理实验室 Lecture 9 Memory Management(1) xlanchen@04/15/2005

计算机系•信息处理实验室

Lecture 9 Memory Management(1)

xlanchen@04/15/2005

xlanchen@04/15/2005 Understanding the Inside of Windows2000

2计算机系信息处理实验室

Two primary tasks

Virtual memory physical memory

Paging

How 2K implements virtual memory?

How it manages the working set?



Contents

Memory Manager Components

Services the Memory Manager Provides

System Memory Pools

Address Space Layout

Address Translation

Page Fault Handling

Virtual Address Descriptors

Working Sets

Page Frame Number Database

Section Objects





Memory Manager

In Ntoskrnl.exe

No parts of the memory manager exist in the HAL

The memory manager is

Fully reentrant



Memory Manager Components

Components:

A set of executive system services

A translation-not-valid and access fault trap handler

Several key components that run in the context of six different kernel-mode system threads



Six system threads

1. Working set manager (priority 16)

Called by the balance set manager

Once per second

When free memory falls below a certain threshold

Drives the overall memory management policies

Working set trimming

Aging

Modified page writing



Six system threads

2. Process/stack swapper (priority 23)

In and out

Awakened by the balance set manager and the thread-scheduling code in the kernel

When an inswap or outswap operation needs to take place



Six system threads

3. Modified page writer (priority 17)

Writes dirty pages on the modified list back to the appropriate paging files

Awakened when the size of the modified list needs to be reduced



Six system threads

4. Mapped page writer (priority 17)

Writes dirty pages in mapped files to disk

Awakened when the size of the modified list needs to be reduced

or

If pages for mapped files have been on the modified list for more than 5 minutes.



Six system threads

5. Dereference segment thread (priority 18)

Responsible for system cache and page file growth and shrinkage.

6. Zero page thread (priority 0)



Configuring the Memory Manager HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management

ClearPageFileAtShutdown

DisablePagingExecutive

IoPageLockLimit

LargePageMinimum

LargeSystemCache

NonPagedPoolQuota

NonPagedPoolSize

PagedPoolQuota

PagedPoolSize

SystemPages





Determine System Memory Size

Values

Small: <19 MB

Medium: 20-32 MB

Large: >32 MB if 2K Professional>64 MB if 2K Server

Kernel-mode routines

MmQuerySystemSize

Small, medium, or large

MmIsThisAnNtAsSystem

TRUE for 2K Server; FALSE for 2K Professional



Examining Memory Usage

EXPERIMENT

Viewing System Memory Information



Pmon.exe (in the Windows 2000 Support Tools)

Pstat.exe (in the Platform SDK)



EXPERIMENT

Accounting for Physical Memory Use



System services

The memory manager provides a set of system services to

Allocate/free virtual memory

Share memory between processes

Map files into memory

Flush virtual pages to disk

Retrieve information about a range of virtual pages

Change the protection of virtual pages

Lock the virtual pages into memory



Services exposed through Win32 API

Page granularity virtual memory functions

Virtualxxx

Memory-mapped file functions

CreateFileMapping, MapViewOfFile

Heap functions

Heapxxx

the older interfaces Localxxx and Globalxxx



Services provided by memory manager

Allocating/deallocating physical memory

Locking pages in physical memory for DMA transfers

To

Other kernel-mode components inside the executive

Device drivers

These functions begin with the prefix Mm

Other, for example Ex…



Services in detailed

Reserving and Committing Pages

Locking Memory

Allocation Granularity

Shared Memory and Mapped Files

Protecting Memory

Copy-on-Write

Heap Functions

Address Windowing Extensions



Reserving and Committing Pages

Reserved address space

To reserve a range of virtual addresses for future use

If accessed, an access violation will occur

Committed pages

either private and not shareable

or

mapped to a view of a section

If accessed, ultimately translate to valid pages in physical memory.

Win32 functions

VirtualAlloc and VirtualAllocEx



Locking Memory Pages can be locked in memory in two ways

Using kernel-mode functions

MmProbeAndLockPages, MmLockPagableCodeSection, MmLockPagableDataSection, or MmLockPagableSectionByHandle.

Pages remain in memory until explicitly unlocked

Using Win32 function

VirtualLock

Lock pages in the process working set.

May paging



Allocation Granularity

Each region begins on an integral boundary

System value: allocation granularity (e.g. 64KB)

GetSystemInfo

Not for kernel-mode code

May be a single-page granularity

The size of the region is

n X (system page size)



Shared Memory and Mapped Files

To share memory among processes and the OS

For example:

Two processes share the same DLL

Sharing mode

Execute-only

Copy-on-write



Section objects

File mapping objects (Win32 API)

CreateFileMapping

OpenFileMapping

…



Protecting Memory

Kernel mode VS. user mode

Each process: a separate private address space

Hardware-controlled memory protection

Read/write, read-only, …

Standard ACLs for shared memory section objects

2K is a robust, reliable OS



Copy-on-Write

before

after



Heap Functions

A heap

A region of one or more pages of reserved address space that can be subdivided and allocated in smaller chunks by the heap manager.

The heap manager

A set of functions that can be used to allocate and deallocate variable amounts of memory

The functions (in Ntdll.dll/Ntoskrnl.exe)



Address Windowing Extensions



System Memory Pools

two types of dynamically sized memory pools

Nonpaged pool

Paged pool

Look-Aside Lists

Driver Verifier



Address Space Layout



User Address Space Layout

0x0 ~ 0xFFFF 64 KB No-access region to aid programmers in avoiding incorrect pointer references

0x10000 ~ 0x7FFEFFFF 2GB -192KB The private process address space.

0x7FFDE000~0x7FFDEFFF 4 KB TEB for first thread.

0x7FFDF000~0x7FFDFFFF 4 KB PEB

0x7FFE0000~0x7FFE0FFF 4 KB Shared user data page

0x7FFE1000~0x7FFEFFFF 60 KB No-access region

0x7FFF0000~0x7FFFFFFF 64 KB No-access region that prevents threads from passing buffers that straddle the user/system space boundary



System Address Space Layout



Address Translation



Translating a Virtual Address

Components of a 32-bit virtual address on x86 systems



Translating a valid virtual address (x86-specific)



Page Directories Each process has a single page directory

The physical address of the process page directory is stored in the kernel process (KPROCESS) block

but is also mapped virtually at address 0xC0300000 on x86 systems (0xC06000000 on systems running the PAE kernel image).

All code running in kernel mode references virtual addresses, not physical ones

CR3 on x86 systems

page directory entries



Process and System Page Tables

page table

system page table

not all processes have the same view of system space

page fault



System & process-private page tables



Page Table Entries



Translation Look-Aside Buffer



Physical Address Extension

PAE

allows access to up to 64 GB of physical memory

The third level—page directory pointer table



Documents

计算机系 信息处理实验室 Lecture 9 Memory Management(1) xlanchen@04/15/2005

计算机系信息处理实验室 Lecture 9 Memory Management(1) xlanchen@04/15/2005