Lecture 10 Memory Management(2)

计算机系•信息处理实验室

Lecture 10 Memory Management(2)

xlanchen@04/22/2005

xlanchen@04/22/2005 Understanding the Inside of Windows2000

2计算机系信息处理实验室

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



Page Fault Handling

Page fault||Kernel trap handler

||Memory manager: fault

handler



Page fault conditions

Page fault can be caused by a variety of conditions

See table 7-14



4 basic invalid PTEs

Page file

The desired page resides within a paging file. An in-page operation is initiated




Demand zero

A page of zeros

The pager : zero page list||free list

||standby list

PTE format : zeros the page file number and offset in the former format




Transition

The desired page is in memory

the standby, modified, or modified-no-write list

The page is removed from the list and added to the working set




Unknown

The PTE is zero, or

The page table doesn't yet exist.



Prototype PTEs

For shared pages

Prototype page table entries

Section objects : an array of prototype PTEs

First reference:

Prototype PTE real PTE

Reference counter in PFN database

0invalid the shared page



Prototype PTEs

Structure of an invalid PTE that points to the prototype PTE

States of a shared page

Active/valid; transition; modified-no-write;demand zero; page file; mapped file

Lazy updating



Two virtual pages (valid/invalid)



In-Paging I/O

Reading a file to satisfy a page fault

In-page I/O operation

Synchronous

not interruptible by APC



Collided page faults

The currently being in-paged page is faulted by another thread or process

A wait operation is issued

When the I/O completes, all threads will be satisfied



Page files

Page files

To store modified pages because of modified page writing

2K supports up to 16 paging files

EXPERIMENT

Viewing system page files

Viewing Page File Usage with Task Manager




Lazy evaluation

Copy-on-write

Demand paging

Page table constructing

Advantages and disadvantages






EXPERIMENT

Viewing Virtual Address Descriptors



Working Sets

Working Set

A subset of virtual pages resident in physical memory

Two types

Process working sets

System working set



Paging Policies How (or when) paging is performed

fetch policy

placement policy

replacement policy



Fetch policy

When

Eager-paging (Before needed)

Demand-paging (Until needed)

2K

Demand-paging + ….

to minimize the number of paging I/Os



Page Fault Read Clustering Values

Memory Size

Cluster Size for Code Pages in Images

Cluster Size for Data Pages in Images

Cluster Size for All Other

Pages

< 12 MB 3 2 5

12-19 MB 3 2 5

> 19 MB 8 4 8



Placement policy

Where

the size of CPU memory caches must be considered

to minimize unnecessary thrashing of the cache



Replacement policy

Which

Which virtual page must be removed from memory to make room for the new page

Include

LRU

FIFO

…

Global or local



2K replacement policy

For multiprocessor system

a variation of a local FIFO

For uniprocessor system

Similar to LRU



Working Set Management Default Minimum and Maximum Working Set Sizes

To change:

SetProcessWorkingSetSize

Memory Size

Default Minimum

Working Set Size (in Pages)

Default Maximum

Working Set Size (in Pages)

Small 20 45

Medium 30 145

Large 50 345Maximum value must < system value

MmMaximumWorkingSetSize



Working set management

When paging, it examines

the process's working set limits

and the amount of free memory

When MmAvailablePages <= MmMinimumFreePages

Must trimming working set (working set manager is called)

Working set manager determines

which

how many



Working Set-Related System Control Variables

Variable Value

MmWorkingSetSize-Increment 6

MmWorkingSetSize-Expansion 20

MmWsExpandThreshold 90

MmPagesAboveWsMinimum Dynamic

MmPagesAboveWsThreshold 37

MmWsAdjustThreshold 45

MmWsTrimReductionGoal 29



EXPERIMENT

Viewing Process Working Set Sizes

Viewing the Working Set List



Balance Set Manager and Swapper

Balance set manager

A system thread for

Working set expansion and trimming

Routine: KeBalanceSetManager

Two event

1-second timer expiring

Internal working set manager



Balance set manager

Every fourth time wakes up swapper

Swapper: routine (KeSwapProcessOrStack)

Checks look-aside lists and adjusts their depths

Looks for priority boosted threads

Calls the working set manager



Swapper

Called by

Balance set manager

Or scheduling code

Looks for threads that can be swapped out

And swapped in some threads



System Working Setfive kinds of pages

System cache pages

Paged pool

Pageable code and data in Ntoskrnl.exe

Pageable code and data in device drivers

System mapped views (sections mapped at 0xA0000000, such as Win32k.sys)



System Working Set Performance Counters

Performance Counter (in Bytes)

System Variable (in Pages)

Memory: Cache Bytes

MmSystemCacheWs.WorkingSetSize

Memory: Cache Bytes Peak

MmSystemCacheWs.Peak

Memory: System Cache Resident

Bytes

MmSystemCachePage

Memory: System Code Resident Bytes

MmSystemCodePage

Memory: System Driver Resident

Bytes

MmSystemDriverPage

Memory: Pool Paged Resident Bytes

MmPagedPoolPage



System Working Set

Minimum and Maximum Size

Memory Size

Minimum (in Pages)

Maximum (in Pages)

Small 388 500

Medium 688 1150

Large 1188 2050



Page Frame Number Database

the page frame number (PFN) database describes the state of each page in physical memory.

States include

Active/Transition/Standby/Modified/Modified no-write/Free/Zeroed/Bad

The PFN database consists of an array of structures that represent each physical page of memory on the system.



Page tables & PFN database



Page lists in PFN database



EXPERIMENT

Viewing the PFN Database



Page List Dynamics state diagram for page frame transitions



EXPERIMENT

Viewing Page Fault Behavior



Modified Page Writer

writing pages back to disk, include two system threads

MiModifiedPageWriter

To paging file

MiMappedPageWriter

To mapped files

The modified page writer event is triggered by

the number of modified pages > MmModifiedPageMaximum

Or MmAvailablePages < MmMinimumFreePages



Modified Page Writer Values

Memory Size Modified Page Threshold

Retain Modified Pages

< 12 MB 100 40

12-19 MB 150 80

19-33 MB 300 150

>33 MB (special case)

400 800



PFN Data Structures

The states of a PFN entry



Flags Within PFN Database Entries

Modified state

Prototype PTE

Parity error

Read in progress

Write in progress

Start of nonpaged pool

End of nonpaged pool

In-page error



Section Objects

section object can be mapped to the paging file or to another file on disk.

Section objects, like other objects, are allocated and deallocated by the object manager



A section object



Internal section structures



EXPERIMENT

Viewing Section Objects

Viewing Control Areas

Documents

Lecture 10 Memory Management(2)