Operating Systems – Memory Management - Computer Engineering
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Transcript of Operating Systems Memory management. Memory Management List of Topics 1. Memory Management 2. Memory...
Operating SystemsOperating Systems
Memory managementMemory management
Memory ManagementMemory Management
List of Topics
1. Memory Management
2. Memory In Systems Design
3. Binding Times
4. Introduction to Memory Management
5. Raw Memory Model
6. Single User Contiguous Memory
7. Relocation - Why and How
8. Overlay Management
List of Topics
1. Memory Management
2. Memory In Systems Design
3. Binding Times
4. Introduction to Memory Management
5. Raw Memory Model
6. Single User Contiguous Memory
7. Relocation - Why and How
8. Overlay Management
Topics (continued)
9. Protection
10. Fixed Partitions
11. Nonuniform Sized Fixed Partitions
12. Uniformly Sized Fixed Partitions
13. Simple Paging
14. Benefits of Simple Paging
15. Page Tables
16. Translation Lookaside Buffers
17. Hierarchical Address Caching
Topics (continued)
9. Protection
10. Fixed Partitions
11. Nonuniform Sized Fixed Partitions
12. Uniformly Sized Fixed Partitions
13. Simple Paging
14. Benefits of Simple Paging
15. Page Tables
16. Translation Lookaside Buffers
17. Hierarchical Address Caching
Topics (continued)
18. Dynamic Partitions
19. Fragmentation
20. Internal Fragmentation
21. External Fragmentation
22. Coalescing Holes
23. Compaction
24. Dynamic Partition Placement
25. Simple Segmentation
26. Memory Layout of A C Program
Topics (continued)
18. Dynamic Partitions
19. Fragmentation
20. Internal Fragmentation
21. External Fragmentation
22. Coalescing Holes
23. Compaction
24. Dynamic Partition Placement
25. Simple Segmentation
26. Memory Layout of A C Program
Topics (continued)
27. malloc
28. sbrk
29. Memory Hierarchy
Topics (continued)
27. malloc
28. sbrk
29. Memory Hierarchy
Memory In Systems designMemory In Systems design
CPU memoryI/O
System
Figure 1: memory Connects CPU and Peripherals
Figure 1: memory Connects CPU and Peripherals
Binding TimesBinding Timessource
program
compiler orassembler
objectmodel
compiletime
linkage editor
load module
loader
Otherobject
modules
system library
loadtime
in-memorybinary
memoryimage
dynamicallyloaded system
library
executiontime
(run time)
Introduction to Memory ManagementIntroduction to Memory Management
Memory management issues:
1. Relocation
2. Protection
3. Sharing
4. Logical Organization
5. Physical Organization
Consider a series of solutions starting
with the most primitive first
Memory management issues:
1. Relocation
2. Protection
3. Sharing
4. Logical Organization
5. Physical Organization
Consider a series of solutions starting
with the most primitive first
Raw Memory ModelRaw Memory Model
The raw memory provides no services
and gives the programmer complete
control.
The raw memory provides no services
and gives the programmer complete
control. 0
1 MB
Figure 3: Raw Machine Model
Figure 3: Raw Machine Model
Single User Contiguous MemorySingle User Contiguous Memory
Primitive operating systems (such as MS-DOS and CP/M) provide some interfaces to the hardware but not much else in the way of services.
Primitive operating systems (such as MS-DOS and CP/M) provide some interfaces to the hardware but not much else in the way of services.
Single User Contiguous Memory(continued)
Single User Contiguous Memory(continued)
Monitor
User
32K
0
fence register
Figure 4: Single User Contiguous MemoryFigure 4: Single User Contiguous Memory
Relocation - Why and HowRelocation - Why and How
Relocation refers to the ability to store a
program at an arbitrary base memory
address.
Actual memory locations have physical
or absolute addresses, user program's
access these locations using logical
addresses.
Relocation refers to the ability to store a
program at an arbitrary base memory
address.
Actual memory locations have physical
or absolute addresses, user program's
access these locations using logical
addresses.
Relocation - Why and How (continued)
Relocation - Why and How (continued)
+CPU
14000
memory
Base register
Logical address
346
Physical address
14346
Figure 5: Address TranslationFigure 5: Address Translation
Overlay ManagementOverlay Management
Overlays have gone out of fashion with
cheaper memory, users (and compilers)
determine which code to swap in and out.
Overlays have gone out of fashion with
cheaper memory, users (and compilers)
determine which code to swap in and out.
symboltable
commonroutines
overlaydriver
pass 1 pass 2
20K
30K
10K
80K70K
Figure 6:OverlayManagementExample [2]
Figure 6:OverlayManagementExample [2]
ProtectionProtection
It is undesirable to permit user programs
(accidentally or intentionally) to accesses
memory outside of their partition.
It is undesirable to permit user programs
(accidentally or intentionally) to accesses
memory outside of their partition.
Protection (continued)Protection (continued)
Monitor
User
32K
0
fence register
Figure 7:Protectionin Resident
MonitorModel
Figure 7:Protectionin Resident
MonitorModel
Fixed PartitionsFixed Partitions
Fixed partitioning refers to memory being
split into contiguous non overlapping
regions of precomputed sizes.
Fixed sized partitions make the selection
of a partition for a job easy.
Fixed partitioning refers to memory being
split into contiguous non overlapping
regions of precomputed sizes.
Fixed sized partitions make the selection
of a partition for a job easy.
Nonuniform Sized Fixed PartitionsNonuniform Sized Fixed Partitions
Fixed Partitions may have differing sizes.Fixed Partitions may have differing sizes.
Operatingsystem
NewProcess
Figure 8:Nonuniform
fixed Partitions [3]
Figure 8:Nonuniform
fixed Partitions [3]
Uniformly Sized Fixed PartitionsUniformly Sized Fixed Partitions
Memory is frequently partitioned into
uniformly sized regions.
Memory is frequently partitioned into
uniformly sized regions.
Operatingsystem512 K
512 K
512 K
512 K
512 K
512 K
512 K
512 K
Figure 9:UniformFixed PartitionAllocation [3]
Figure 9:UniformFixed PartitionAllocation [3]
Simple PagingSimple Paging
Paging provides relocation, and splits
memory into fixed length partitions
called frames.
Paging provides relocation, and splits
memory into fixed length partitions
called frames.
Page frame 0
Page frame 1
Page frame 2
Page frame 3
0
p-1p
2p-12p
3p-13p
4p-1
Figure 10:SimplePaging
[1]
Figure 10:SimplePaging
[1]
4p
5p-15p
6p-16p
7p-17p
8p-1
Page frame 4
Page frame 5
Page frame 6
Page frame 7
Figure 10:SimplePaging(continued)
[1]
Figure 10:SimplePaging(continued)
[1]
Pageframe
number
01234567
Pageframesize
pppppppp
Range of realstorage
addresses
0 p-1p 2p-12p 3p-13p 4p-14p 5p-15p 6p-16p 7p-17p 8p-1
Benefits of Simple PagingBenefits of Simple Paging
Simple paging allows discontiguous
storage for memory objects exceeding
the page frame size.
Simple paging allows discontiguous
storage for memory objects exceeding
the page frame size.
Virtualmemory
...
...
Addressmapping
mechanism
Realstorage
Contiguousvirtual
storagelocations
Page TablesPage Tables
One simple mechanism is to allocate
some real memory space for a table, and
hash page addresses using the high
order address bits as pointers into the
page table. There are 2 real memory
accesses per virtual memory access.
One simple mechanism is to allocate
some real memory space for a table, and
hash page addresses using the high
order address bits as pointers into the
page table. There are 2 real memory
accesses per virtual memory access.
Page Tables (continued)Page Tables (continued)
d
b
p
p1 dp1
p
bPage # Displacement
Virtual address} v=(p,d)
Page
bMap Table
p
}Real
address
b+p
Translation Lookaside BuffersTranslation Lookaside Buffers
Translation lookaside buffers (TLB)
eliminate one physical memory reference
using special associative memory, which
addressed by its contents in O(1) parallel
search time.
Translation lookaside buffers (TLB)
eliminate one physical memory reference
using special associative memory, which
addressed by its contents in O(1) parallel
search time.
d }Virtual addressV=(p,d)
p p1
Page # Displacement
p
p1 d }Real
Address r
Frame # Displacement
Associative map
Associative Memory LookupAssociative Memory Lookup
Hierarchical Address CachingHierarchical Address Caching
Rather than placing all addresses in the
TLB recently/frequently used addresses
are stored in associative memory, with
misses being serviced by the page table.
Rather than placing all addresses in the
TLB recently/frequently used addresses
are stored in associative memory, with
misses being serviced by the page table.
Hierarchical Address Caching (continued)Hierarchical Address Caching (continued)
Address ofPage table b
Page tableorigin register
p1
Page #p
Displacement
d
Virtual address v=(p,d)
+
Partial associative
p p1
p
Try this first
Performed only if no match in associative map b+p Real address
Displacementd
Frame# p1
Only if match in associative map
Only if no match in associative map
Direct map (all pages)
Map (most active pages only
Dynamic PartitionsDynamic Partitions
Dynamically partitioned memory allows
placement of relocatable code in variable
size contigous memory regions.
Dynamically partitioned memory allows
placement of relocatable code in variable
size contigous memory regions.
Dynamic Partitions (continued)Dynamic Partitions (continued)
user needs
IHGFEDCBA
9K.18K.11K.32K.14K.25K.10K.20K.15K.
Operatingsystem
UserA 15K
Operating
User
User
UserUser
User
User
User
User
User
Operating Operatingsystem systemsystem
Free
B 20K
A 15KA 15KA 15K
B 20K B 20K
FreeFree
C 10K C 10K
D 25KFree
FragmentationFragmentation
Fragmentation makes available memory useless by breaking it into discontiguous pieces too small to use.
Fragmentation makes available memory useless by breaking it into discontiguous pieces too small to use.
Fragmentation (continued)Fragmentation (continued)
There are two categories of memory
fragmentation:
1. Internal Fragmentation --- A fixed partition contains more memory than required by the user, and some is wasted.
2. External Fragmentation --- Results from the holes left by dynamic partitions.
There are two categories of memory
fragmentation:
1. Internal Fragmentation --- A fixed partition contains more memory than required by the user, and some is wasted.
2. External Fragmentation --- Results from the holes left by dynamic partitions.
Internal FragmentationInternal Fragmentation
Internal fragmentation occurs when fixed
size partitions are too large.
Internal fragmentation occurs when fixed
size partitions are too large.
Pag
e 2
Pag
e 1
Pag
e 0
Inte
rna
lfr
ag
me
nta
tio
n
Logical AddressPage#=1,Offset=478
000001 01110111110
478
Figure 16:InternalFragmentation[3]
Figure 16:InternalFragmentation[3]
External FragmentationExternal Fragmentation
External fragmentation happens when
dynamic partitions are released. The
fragments are frequently called holes.
External fragmentation happens when
dynamic partitions are released. The
fragments are frequently called holes.
operatingsystem
User A
User B
User C
User D
User E
Hole
operatingsystem
User A
User C
User D
User E
Hole
operatingsystem
User A
User C
User E
Hole
Hole Hole
Hole
User B finishes and frees its storage. User D
finishes and frees its storage.
Coalescing HolesCoalescing Holes
Adjacent holes in dynamic partitions
should be coalesced into a single larger
hole.
Adjacent holes in dynamic partitions
should be coalesced into a single larger
hole.
operatingsystem
other users
5K user A
otherusers
2K Hole 2K Hole
5K Hole
otherusers
other users
operatingsystem
7K Hole
otherusers
other users
operatingsystem
User A finishes and frees its storage
Operating system combines adjacent
holes to form a single larger hole.
CompactionCompaction
If the amount of memory available in the
holes is large enough to service a
request, the holes may made contiguous
by compacting storage.
If the amount of memory available in the
holes is large enough to service a
request, the holes may made contiguous
by compacting storage.
operatingsystems
In use
In use
In use
Free
Free
Free
operatingsystems
Free
In use
In use
In use
Operating system places all “in use” blocks together leaving free storage as a single, large hole.
(a) First-Fit Strategy
Place job in first storage hole on free storage place list in which it will fit
(a) First-Fit Strategy
Place job in first storage hole on free storage place list in which it will fit
Dynamic Partition PlacementDynamic Partition Placement
Operating systems
16K hole
14K hole
5K hole
30K hole
In use
In use
In use
a 16K
c 14K
e 5K
g 30K...
Request for 13K
Free Storage List
Start Address
Length
(kept in storage address order, or something in random order.)
0
a
b
c
d
e
f
g
h
(b) Best-Fit Strategy
Place job in the smallest possible hole in which it will fit.
(b) Best-Fit Strategy
Place job in the smallest possible hole in which it will fit.
Operating systems
16K hole
14K hole
5K hole
30K hole
In use
In use
In use
e 5K
c 14K
a 16K
g 30K...
Request for 13KStart
Address Length
(Kept in ascending order by hole size.)
0
a
b
c
d
e
f
g
h
Free Storage List
(c) Worst-Fit Strategy
Place job in the largest possible hole in which it will fit.
(c) Worst-Fit Strategy
Place job in the largest possible hole in which it will fit.
Operating systems
16K hole
14K hole
5K hole
30K hole
In use
In use
In use
g 30K
a 16K
c 14K
e 5K...
Request for 13KStart
Address Length
(Kept in descending order by hole size.)
0
a
b
c
d
e
f
g
h
Free Storage List
Simple SegmentationSimple Segmentation
Segmentation provides relocation, and
supports contiguous variable length
partitions.
Segmentation often provides
protection (counterexample Intel 8086).
Segmentation provides relocation, and
supports contiguous variable length
partitions.
Segmentation often provides
protection (counterexample Intel 8086).
CPU <
Logical address
no
Trap; address error
+yes
limit base
memory
Memory Layout of A C ProgramsMemory Layout of A C Programs
Traditional Unix/C memory images of
programs use segments.
Traditional Unix/C memory images of
programs use segments.
high address
low address text
uninitialized data(bss)
heap
stack
Initialized data
Command-line arguments and environment variables
initialized to zero by exec
read from program file by exec
mallocmalloc
Programmers often want to allocate data objects which persist beyond the function call creating them (e.g. constructors in OOP).
In C and C++ the malloc operator maintains a linked list of data objects, in the user program's Data segment (on the Heap).
Programmers often want to allocate data objects which persist beyond the function call creating them (e.g. constructors in OOP).
In C and C++ the malloc operator maintains a linked list of data objects, in the user program's Data segment (on the Heap).
user data
user data
user data
user data
user data
user data
In Use List
Free List
Key
Memory management Information
sbrksbrk
A user program can exhaust its default
heap space allocation.
The Unix sbrk system call increases data
segment allocation at run time.
A user program can exhaust its default
heap space allocation.
The Unix sbrk system call increases data
segment allocation at run time.
Memory allocationfunction malloc
applicationcode
sbrksystem call
kernel
userprocess
Memory HierarchyMemory Hierarchy
Users want to:
1. Increase their address space, using slow cheaper memory to extend their more expensive faster memory.
2. Increase the speed at which they can the extended memory by using small amounts of expensive fast memory.
Users want to:
1. Increase their address space, using slow cheaper memory to extend their more expensive faster memory.
2. Increase the speed at which they can the extended memory by using small amounts of expensive fast memory.
Memory HierarchyMemory Hierarchy
Registers
Cache
Main Memory
Magnetic Disk (Cache)
Backups Optical Juke Box Remote Access
