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Lecture
7:
Memory
Management

CSE
120:
Principles
of
Opera>ng
Systems


UC
San
Diego:
Summer
Session
I,
2009

Frank
Uyeda


Announcements

• PeerWise
ques>ons
due
tomorrow.

• Project
2
is
due
on
Friday.

– Milestone
on
Tuesday
night.


• Homework
3
is
due
next
Monday.


2


Goals
for
Today

• Mo>va>on
for
Memory
Management

• Understand
Paging

– How
to
translate
from
virtual
to
physical
address

– Determine
size,
structure
of
page
tables


3


Memory
Management

• Goals
of
memory
management


– Provide
a
convenient
abstrac>on
for
programming

– Allocate
scarce
memory
resources
among
compe>ng
 processes – Maximize
performance
with
minimal
overhead


• Mechanisms


– Physical
and
virtual
addressing

– Techniques:
Par>>oning,
paging,
segmenta>on

– Page
table
management,
TLBs,
VM
tricks


• Policies


– Page
replacement
algorithms

4


In
the
beginning…..

Physical
Memory


• Batch
programmed
systems

– Programs
use
physical
 addresses directly

– OS
loads
job,
runs
it,
unloads
it

– Similar
to
what
nachos
does
 right now



Stack

SP


Heap

Data
Segment







(you’ll
change
this
in
Project
2)

PC


Text
Segment


Opera>ng
System

5


Let
there
be
Mul>programming

• Mul>programming
changes
all
of
this

– Want
mul>ple
processes
in
memory
at
once

• Overlap
I/O
and
CPU
of
mul>ple
jobs


– Can
do
it
a
number
of
ways

• Fixed
and
variable
par>>oning,
paging,
segmenta>on


– Requirements

• Need
protec>on
–
restrict
which
addresses
jobs
can
use

• Fast
transla>on
–
lookups
need
to
be
fast

• Fast
changes
–
upda>ng
memory
hardware
on
context
 switch 6


Virtual
Memory

• The
basic
abstrac>on
provided
by
the
OS
memory
 management is
virtual
memory

– A
process’s
address
space

in
memory
is
not
necessarily
 the same
as
the
physical
memory
(RAM)
address
in
which
 it resides

– When
a
process
requests
a
memory
address,
the
OS
will
 translate the
address
from
a
virtual
address
to
a
physical
 address. 7


Virtual
Addresses

• Processes
access
memory
using
a
virtual
address

– The
virtual
address
is
not
the
same
as
the
physical
RAM
address
in
which
it
resides

– The
OS
(hardware
MMU)
translates
the
virtual
address
into
the
physical
RAM
address

– Who
determines
the
mapping
for
the
transla>on?


0xFFF…..
(Ending
Address)


Stack


SP

Address
Space


Heap

Data
Segment


PC

0x00…….
(Star>ng
Address)


Text
Segment

8


Virtual
Addresses

• Processes
access
memory
using
a
virtual
address


– The
virtual
address
is
not
the
same
as
the
physical
RAM
address
in
which
it
resides

– The
OS
(hardware
MMU)
translates
the
virtual
address
into
the
physical
RAM
address

– Who
determines
the
mapping
for
the
transla>on?

Virtual
Memory


0xFFF…..
(Ending
Address)


Physical
Memory


Stack


Stack


SP


…..


MMU


Address
Space


Heap

Data
Segment

PC

0x00…….
(Star>ng
Address)


Heap

Data
Segment


Text
Segment


Text
Segment

9


Virtual
Addresses

• Processes
access
memory
using
a
virtual
address


– The
virtual
address
is
not
the
same
as
the
physical
RAM
address
in
which
it
resides

– The
OS
(hardware
MMU)
translates
the
virtual
address
into
the
physical
RAM
address

– Who
determines
the
mapping
for
the
transla>on?

Virtual
Memory


0xFFF…..
(Ending
Address)


Physical
Memory


Text
Segment


Stack


SP


Heap

MMU


Address
Space


Data
Segment


Heap


PC

0x00…….
(Star>ng
Address)


Text
Segment


…..


Data
Segment


Stack

10


Virtual
Memory

• Virtual
memory
enables
programs
to
execute
without
 requiring their
en>re
address
space
reside
in
physical
memory

– Saves
space

• Many
programs
do
not
need
all
of
their
code
and
data
at
once
(or
ever),
 so there
is
no
need
to
allocate
memory
for
it


– Allows
flexibility
for
applica>on
and
OS

• Indirec>on
allows
moving
programs
around
in
memory;
OS
can
adjust
 amount of
memory
allocated
based
upon
its
run‐>me
behavior

• Allows
processes
to
address
more
or
less
memory
than
physically
installed
 in the
machine


– Isola>on
and
protec>on

• One
process
cannot
access
memory
addresses
in
others


• Excep>on:
shared
memory,
which
we’ve
already
covered

11


Memory
Management
Requirements

• Protec>on

– Restrict
which
physical
addresses
processes
can
use,
so
 they can’t
stomp
on
each
other


• Fast
transla>on

– Accessing
memory
must
be
fast,
regardless
of
the
 protec>on scheme


• Fast
context
switching

– Overhead
of
upda>ng
memory
hardware
on
a
context
 switch must
be
low


• Requires
hardware
support
for
efficient
implementa>on

12


MMU
and
TLB



Memory
Management
Unit
(MMU)

– Hardware
unit
that
translates
a
virtual
address
to
a
physical
address

– Each
memory
reference
is
passed
through
the
MMU

– Translate
a
virtual
address
to
a
physical
address




Transla>on
Lookaside
Buffer
(TLB)

– Essen>ally
a
cache
for
the
MMU’s
virtual‐to‐physical
transla>ons
table

– Not
needed
for
correctness
but
source
of
significant
performance
gain


Virtual
Address

CPU


MMU


Transla>on

Table


Physical


Address


Memory


TLB

13


Memory
Alloca>on

• How
should
we
allocate
memory
to
 processes? Physical
Memory


MMU


14


Fixed
Par>>ons

• Physical
memory
is
broken
up
into
fixed
par>>ons

Physical
Memory

– Hardware
requirements:
base
register

– Physical
address
=
virtual
address
+
base
register


P1

P2


Base
Register

P4’s
Base


P3

Virtual
Address

Offset


+


P4

P5


15


Fixed
Par>>ons

• Physical
memory
is
broken
up
into
fixed
par>>ons







Hardware
requirements:
base
register

Physical
address
=
virtual
address
+
base
register

Base
register
loaded
by
OS
when
it
switches
to
a
process

Size
of
each
par>>on
is
the
same
and
fixed

How
do
we
provide
protec>on?


• Advantages


– Easy
to
implement,
fast
context
switch


• Problems


– Internal
fragmenta>on:
memory
in
a
par>>on
not
used
by
a
 process is
not
available
to
other
processes

– Par>>on
size:
one
size
does
not
fit
all
(very
large
processes?)


16


Variable
Par>>ons

• Natural
extension
–
physical
memory
is
broken
up
into
 variable sized
par>>ons

– Hardware
requirements:
base
register
and
limit
register

– Physical
address
=
virtual
address
+
base
register

– Why
do
we
need
the
limit
register?
Protec>on

• If
(physical
address
>
base
+
limit)
then
protec>on
fault


17


Variable
Par>>ons

Physical
Memory


Base
Register

P4’s
Base


P1

P2


Limit
Register

P3’s
Base

Virtual
Address

Offset


Yes?


on
Fault

18


Variable
Par>>ons

• Natural
extension
–
physical
memory
is
broken
up
into
 variable sized
par>>ons

– Hardware
requirements:
base
register
and
limit
register

– Physical
address
=
virtual
address
+
base
register

– Why
do
we
need
the
limit
register?
Protec>ons

• If
(physical
address
>
base
+
limit)
then
excep>on
fault


• Advantages

– No
internal
fragmenta>on:
allocate
just
enough
for
process


• Problems

– External
fragmenta>on:
job
loading
and
unloading
 produces empty
holes
scapered
throughout
memory

19


Paging

• Paging
solves
the
external
fragmenta>on
problem
by
using
fixed
sized
 units in
both
physical
and
virtual
memory

Physical
Memory

Virtual
Memory

Page
1

Page
1

Page
2

Page
2


…..


Page
3

Page
4


Page
N

Page
5

20


User/Process
Perspec>ve

• Users
(and
processes)
view
memory
as
one
con>guous
 address space
from
0
to
N

– Virtual
address
space


• In
reality,
pages
are
scapered
throughout
physical
storage

• The
mapping
is
invisible
to
the
program

• Protec>on
is
provided
because
a
program
cannot
reference
 memory outside
of
its
virtual
address
space

– The
address
“0x1000”
maps
to
different
physical
addresses
in
different
 processes 21


Paging

• Transla>ng
addresses






Virtual
address
has
two
parts:
virtual
page
number
and
offset

Virtual
page
number
(VPN)
is
an
index
into
a
page
table

Page
table
determines
page
frame
number
(PFN)

Physical
address
is
PFN::offset


0xBAADF00D
=

 virtual address


0xBAADF

 virtual page
number


0xBAADF



0x00D


virtual
page
number


offset


Transla>on

Table

page
table


0x900DF

 physical page
number

(page
frame
number)


22


Page
Lookups

Physical
Memory


0xBAADF00D


0x00000000


Virtual
Address

Page
number


0xBAADF


Offset


0xF00D


Page
1

Physical
Address


Page
2


Page
frame


Page
Table


0x900DF


0xF00D


Page
3

0x900DF00D


…..


Page
frame


Offset


Page
N

0xFFFFFFFF

23


Paging

• Transla>ng
addresses






Virtual
address
has
two
parts:
virtual
page
number
and
offset

Virtual
page
number
(VPN)
is
an
index
into
a
page
table

Page
table
determines
page
frame
number
(PFN)

Physical
address
is
PFN::offset


• Page
tables

– Map
virtual
page
number
(VPN)
to
page
frame
number
(PFN)

• VPN
is
the
index
into
the
table
that
determines
PFN


– One
page
table
entry
(PTE)
per
page
in
virtual
address
space

• Or,
one
PTE
per
VPN


24


Paging
Example

• Memory
address
is
32
bits

• Pages
are
4K

– VPN
is








bits
(






VPNs),
offset
is






bits


• Virtual
address
is
0x7468

– Virtual
page
is







,
offset
is
_______





• Page
table
entry







contains
0x2

– Page
frame
base
is
0x2

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...Wiki Loves Monuments: Photograph a monument, help Wikipedia and win! Production theory From Wikipedia, the free encyclopedia Jump to: navigation, search Production theory is the study of production, or the economic process of converting inputs into outputs. Production uses resources to create a good or service that is suitable for use, gift-giving in a gift economy, or exchange in a market economy. This can include manufacturing, storing, shipping, and packaging. Some economists define production broadly as all economic activity other than consumption. They see every commercial activity other than the final purchase as some form of production. Production is a process, and as such it occurs through time and space. Because it is a flow concept, production is measured as a “rate of output per period of time”. There are three aspects to production processes: 1. the quantity of the good or service produced, 2. the form of the good or service created, 3. The temporal and spatial distribution of the good or service produced. A production process can be defined as any activity that increases the similarity between the pattern of demand for goods and services, and the quantity, form, shape, size, length and distribution of these goods and services available to the market place. Contents * 1 Neoclassical Theory of Production * 1.1 Factors of production * 1.2 Total, average, and marginal product * 1.3 Diminishing returns * 1.4 Diminishing marginal returns...

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...Website: www.bangladesh-bank.org www.bangladeshbank.org.bd www.bb.org.bd Banking Regulation & Policy Department Bangladesh Bank Head Office Dhaka BRPD Circular No.02 Date: February 27, 2011 ---------------------Falgun 15, 1417 Chief Executives All Scheduled Banks in Bangladesh Policy Guidelines for Green Banking Introduction: We are aware that global warming is an issue that calls for a global response. The rapid change in climate will be too great to allow many eco-systems to suitably adapt, since the change have direct impact on biodiversity, agriculture, forestry, dry land, water resources and human health. Due to unusual weather pattern, rising greenhouse gas, declining air quality etc. society demands that business also take responsibility in safeguarding the planet. Green finance as a part of Green Banking makes great contribution to the transition to resource-efficient and low carbon industries i.e. green industry and green economy in general. Green banking is a component of the global initiative by a group of stakeholders to save environment. The state of environment in Bangladesh is rapidly deteriorating. The key areas of environmental degradation cover air pollution, water pollution and scarcity, encroachment of rivers, improper disposal of industrial medical and house-hold waste, deforestation, loss of open space and loss of biodiversity. In addition, Bangladesh is one of the most climate change vulnerable countries. In line with ...

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...Acknowledgements The authors wish to thank the entire OII team for their support of OxIS research. Our particular thanks to Prof. Helen Margetts, Dr Rebecca Eynon and Martin Dimov for their contributions to this report. We also wish to acknowledge Kunika Kono and David Sutcliffe for their design and editorial support of this report. For their early contributions to OxIS we would like to thank Prof. Richard Rose, Dr Adrian Shepherd, and Dr Corinna di Gennaro. All have helped shape the evolution of this research. We are grateful for the support of OxIS 2007 by the Higher Education Funding Council of England (HEFCE) and sponsorship of the OxIS 2007 Survey by The British Library, Cisco, Ofcom, and Talisma. Our colleagues from these sponsoring organisations have made valuable comments, helping to ensure that OxIS continues to address enduring as well as emerging issues of policy and practice. Please cite the source of text and data excerpts as: Dutton, W. and Helsper, E.J. (2007) The Internet in Britain: 2007. Oxford Internet Institute, University of Oxford (Oxford, UK). © The University of Oxford for the Oxford Internet Printed copies can be ordered from the enquiries assistant at: enquiries@oii.ox.ac.uk. Copies cost £5 each (to cover the cost of postage and handling). All orders should be sent along with full payment in UK Pounds Sterling to: Oxford Internet Institute, University of Oxford, 1 St Giles, Oxford OX1 3JS, United Kingdom. Please do not send cash. Cheques should be drawn...

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...Ozone Layer Depletion: Introduction Are we damaging our protective blanket? Sunlight contains some ultraviolet light, and when we expose ourselves to too much of it, we get a sunburn. Over time, too much exposure to ultraviolet light can lead to cataracts and skin cancer. The earth has a layer in the upper atmosphere, consisting mostly of ozone gas, that filters out most of the ultraviolet in the sun's radiation. Recently there has been scientific evidence that we have been releasing gases that damage this layer. Our country and others have reacted by invoking legislation that should eliminate these contaminants from the atmosphere.   What does the Ozone Layer do? * Ozone absorbs 99% of the harmful ultraviolet (UV) radiation. Without the Ozone Layer * Most of the harmful UV radiation will penetrate the atmosphere. The Ozone Layer The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone (O3). This layer absorbs 97-99% of the sun's high frequency ultraviolet light, which is potentially damaging to life on earth. Over 90% of ozone in earth's atmosphere is present here "Relatively high" means a few parts per million—much higher than the concentrations in the lower atmosphere but still small compared to the main components of the atmosphere. It is mainly located in the lower portion...

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...BINDURA UNIVERSITY OF SCIENCE EDUCATION FACULTY OF COMMERCE DEPARTMENT OF ECONOMICS COURSE OUTLINE FOR ECONOMIC PRINCIPLES1 – EC101 Lecturers : A.Chingarande (0776326638), F. Tafirei (0772757491) & M. Mzumara (0712737723) Emails : achingarande@buse.ac.zw, ftafirei@buse.ac.zw & mmzumara@buse.ac.zw Consulting Times: Tuesdays and Thursdays 0900 Hrs – 1100Hrs or by appointment Venue : Office No H8 (Clinic Office) Main Campus Course Aims:   Provide a basis of factual knowledge of economics; Encourage the student to develop:  a facility for self-expression, not only in writing but also in using additional aids, such as statistics and diagrams, where appropriate;  the habit of using works of reference as sources of data specific to economics;  the habit of reading critically to gain information about the changing economy we live in; and  an appreciation of the methods of study used by the economist, and of the most effective ways economic data may be analysed, correlated, discussed and presented. Course Objectives:      Demonstrate knowledge and understanding of the specified content; Interpret economic information presented in verbal, numerical or graphical form; Explain and analyse economic issues and arguments, using relevant economic concepts, theories and information; Evaluate economic information, arguments, proposals and policies, taking into consideration relevant information and theory, and distinguishing facts from hypothetical statements and value...

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