stack - Arcos

Transcription

stack - Arcos

ARCOS Group
Universidad Carlos III de Madrid
Lesson 6 (a)
Memory management
Operating System Design
Bachelor in Informatics Engineering
Goals
To know the internal methods for memory
management within an Operating System
To use tools for monitoring, management, and finetuning on Operating Systems.
2
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Alejandro Calderón Mateos
Recommended readings
Base
Additional
Carretero 2007:
1.
1.
Tanenbaum 2006(en):
1.
Chapter 4
1.
Stallings 2005:
2.
1.
Part three
Silberschatz 2006:
3.
1.
3
Chapter 4
Chapter 4
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Remember…
1.
To study the associated theory.
Better study the bibliography readings because the
slides are not enough.
To add questions with answers, and proper
justification.
2.
To review what in class is introduced.
To do the practical Linux task step-by-step.
3.
To practice the knowledge and capacities.
To do the practical tasks as soon as possible.
To do as much exercises as possible.
4
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Overview
1.
Introduction
2.
Process memory regions
3.
How to prepare an executable
4.
Virtual memory support
5
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Overview
1.
Introduction
2.
3.
4.
Executable
File
Application
6
Process
Image2
Image1
Operating
System
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Basic usage of memory
address, value, and size
00
‘a’
01
222
02
0x3F
03
‘&’
…
7
…
Value
Element stored in memory.
Address
Place in memory.
Size
Number of bytes needed to stored the
value.
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00
‘a’
01
222
02
0x3F
03
‘&’
…
8
…
Value
Address
Place in memory.
Size
value.
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00
‘a’
01
222
02
0x3F
03
‘&’
…
9
…
Value
Address
Place in memory.
Size
value.
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functional interface
00
‘a’
01
222
02
0x3F
03
‘&’
Value = read (Address)
write (Address, Value)
Before to access into a address, it must
point to a memory area previously
allocated.
…
10
…
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Introduction
Definitions
Environments
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Introduction
Definitions
Environments
12
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Application and Process
Application: set of data and instruction sequence that is able to
perform a specific task or work.
Disk
Executable
file
13
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Application: set of data and instruction sequence that is able to
perform a specific task or work.
In order to be executed it has to be in memory.
Main memory
Disk
Executable
file
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Process: executing application.
Main memory
Disk
Process1
15
Executable
file
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It is possible that the same application executes several times
(we will found several process in memory)
Main memory
Process2
Disk
Process1
16
Executable
file
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The Operating System is loaded in memory and
it performs the memory management in order to shared the memory
among all process (in a similar way like it does with the CPU).
Main memory
Process2
Disk
Process1
Executable
file
Operating
System
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Process image
Memory image: sequence of memory addresses (and its contents)
allocated for a process.
Main memory
Image2
Process2
Disk
Image1
Process1
Executable
file
Operating
System
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Process image
Memory image: sequence of memory addresses (and its contents)
allocated for a process.
Part of the control information is not in the PCB because efficiency
reasons and sharing reasons.
Main memory
Image2
Process2
Disk
Image1
Process1
Executable
file
Operating
System
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Introduction
Definitions
Environments
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Monoprogramming Systems
memoria
Process
Only one process is executed at a
time.
Memory is shared between the
operating system and the process.
Ej.: MS-DOS, DR-DOS, etc.
Operating System
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Multiprogramming systems
memoria
Process 1
More than one process is kept in
main memory.
It improves the CPU occupancy:
Process blocks -> execute another
Process 2
Process 3
Operating System
22
The memory management work
is basically a constrained
optimization task.
E.g.: Unix, Windows NT, etc.
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memoria
Process 1
More than one process is kept in
main memory.
It improves the CPU occupancy:
Process blocks -> execute another
Process 2
Process 3
Operating System
23
The memory management work
is basically a constrained
optimization task.
E.g.: Unix, Windows NT, etc.
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example of computing the CPU usage
memoria
Process 1
Process 2
Process 3
Operating System
24
p = % of time that a process is blocked
pn = probability of n independent processes
being all blocked
1- pn = probability of CPU not being idle
n = 5 independent process
p = 0,8 of time blocked (20% on CPU)
usage = 5*20% → 100%
usage = 1-0,85 → 67%
1-0,810 → 89%
http://wwwithcs.rutgers.edu/~pxk/416/notes/content/09-memory_management-slides-6.pdf
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example of computing the CPU usage
memoria
Process 1
Process 2
Process 3
Operating System
25
p = % of time that a process is blocked
pn = probability of n independent processes
being all blocked
1- pn = probability of CPU not being idle
n = 5 independent process
p = 0,8 of time blocked (20% on CPU)
usage = 5*20% → 100%
usage = 1-0,85 → 67%
1-0,810 → 89%
http://wwwithcs.rutgers.edu/~pxk/416/notes/content/09-memory_management-slides-6.pdf
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Introduction
summary
Definitions
Environments
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Overview
1.
Introduction
2.
3.
4.
Main memory
stack
Process2
data
code
stack
Process1
data
code
Operating
System
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Logical organization (applications)
process memory model
One process consists of a list of memory
regions.
One region is one contiguous memory
area of the process address space where
all elements have the same properties.
0xFFFF..
stack
Main properties:
Permissions: read, write, and execution.
Shared among threads: private or shared
Size (fixed/variable)
Initial value (with or without support)
Static or dynamic creation
Growth direction
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Sistemas operativos: una visión aplicada
data
code
0x0000..
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Main process regions
code (text)
int a;
int b = 5;
void f(int c) {
int d;
static e = 2;
0xFFFF..
stack
b = d + 5;
.......
return;
}
main (int argc, char **argv) {
char *p;
p = (char *) malloc (1024)
f(b)
.......
free (p)
....
exit (0)
}
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static data
w/o initial val.
static data
with initial val.
code
0x0000..
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code (text)
int a;
int b = 5;
code
• Static (fixed)
• It is known at compilation time.
• Instruction sequence to be executed.
void f(int c) {
int d;
static e = 2;
0xFFFF..
stack
b = d + 5;
.......
return;
}
char *p;
f(b)
.......
free (p)
....
exit (0)
}
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static data
w/o initial val.
static data
with initial val.
code
0x0000..
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data (data)
int a;
int b = 5;
void f(int c) {
int d;
static e = 2;
0xFFFF..
stack
b = d + 5;
.......
return;
}
char *p;
f(b)
.......
free (p)
....
exit (0)
}
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static data
w/o initial val.
static data
with initial val.
code
0x0000..
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data (data)
int a;
int b = 5;
Global variables
• Static (fixed)
• They are allocated when application starts.
• They exits during the execution.
• Fixed address on memory and executable.
void f(int c) {
int d;
static e = 2;
0xFFFF..
stack
b = d + 5;
.......
return;
}
char *p;
f(b)
.......
free (p)
....
exit (0)
}
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static data
w/o initial val.
static data
with initial val.
code
0x0000..
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stack (stack)
int a;
int b = 5;
void f(int c) {
int d;
static e = 2;
0xFFFF..
stack
b = d + 5;
.......
return;
}
char *p;
f(b)
.......
free (p)
....
exit (0)
}
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static data
w/o initial val.
static data
with initial val.
code
0x0000..
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stack (stack)
int a;
int b = 5;
Local variables and parameters
• Dynamics
• They are created on function invocation
• They are destroyed on function call return
• Recursivity: several instances of a variable
void f(int c) {
int d;
static e = 2;
0xFFFF..
stack
b = d + 5;
.......
return;
}
char *p;
f(b)
.......
free (p)
....
exit (0)
}
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static data
w/o initial val.
static data
with initial val.
code
0x0000..
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stack (stack)
int a;
int b = 5;
void f(int c) {
int d;
static e = 2;
b = d + 5;
.......
return;
0xFFFF..
stack
stack’
}
char *p;
f(b)
....... pthread_create(f…)
free (p)
....
exit (0)
}
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static data
w/o initial val.
static data
with initial val.
code
0x0000..
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Code or text
Shared, RX, Fixed Size, executable support
0xFFFF..
stack
Data
With initial value
Shared, RW, Fixed size, executable support
Without initial value
Shared, RW, Fixed size, w/o support (0 filled)
data
Stack
Private, RW,Variable size, w/o support (0 filled)
It grows toward lower addresses.
Initial stack: application arguments.
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code
0x0000..
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0xFFFF..
stack
Heap
Soporte de memoria dinámica (C malloc)
Shared, RW,Variable size, w/o support (0 filled?)
It grows toward higher addresses.
…
Mapped files
Region associated to a mapped file.
Private/Shared, variable size, support on file.
Protection depends on projection.
data
code
0x0000..
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0xFFFF..
stack
Heap
…
Mapped files
data
code
0x0000..
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dynamic data (heap)
int a;
int b = 5;
void f(int c) {
int d;
static e = 2;
b = d + 5;
.......
return;
}
char *p;
f(b)
.......
free (p)
....
exit (0)
}
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0xFFFF..
stack
dynamic
data
static data
code
0x0000..
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dynamic data (heap)
int a;
int b = 5;
Dynamic variable
• Variables with no memory space assigned on
compilation time.
• The memory space is allocated (and free) on
runtime.
void f(int c) {
int d;
static e = 2;
b = d + 5;
.......
return;
}
char *p;
f(b)
.......
free (p)
....
exit (0)
}
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0xFFFF..
stack
dynamic
data
static data
code
0x0000..
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0xFFFF..
stack
Heap
…
Mapped files
data
code
0x0000..
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Memory mapped file
(1/3)
Process
memory
image
Main
memory
Memory
mapped
file
file
swap
One process region is associated with one file.
Some file blocks (pages) are in main memory.
The process gets the file contents like it are consecutively in
memory (access in memory rather than traditional read/write).
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Memory mapped file
(2/3)
void *mmap(void *addr, size_t len, int prot, int flags, int fildes, off_t off);
Set a map between the process address space and the file descriptor or
shared memory object.
It returns the memory address where the maps is.
addr where mapping. If NULL then the O.S. will choose one.
len is the number of bytes to be mapped.
prot type of access (reading, writing, or executing).
flags options for the mapping operation (shared, privated, etc.).
fildes file descriptor of a file or memory object to be mapped.
off offset within the file where the mapping is going to start.
void munmap(void *addr, size_t len);
Unmaps part of the process address space that was mapped on the
addr address.
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Memory mapped file
(3/3)
How many times a character appears in a memory mapped file.
/* 1) To open the file descriptor */
fd=open(argv[2], O_RDONLY));
fstat(fd, &fs); /* Get the file size */
/* 2) To map the file */
org=mmap((caddr_t)0, fs.st_size, PROT_READ, MAP_SHARED, fd, 0));
close(fd); /* close the file descriptor */
/* 3) Access loop */
p=org;
for (i=0; i<fs.st_size; i++)
if (*p++==caracter) contador++;
/* 4) To unmap the file */
munmap(org, fs.st_size);
printf("%d\n", contador);
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Heap
Private, RW,Variable size, w/o support (0 filled?)
0xFFFF..
stack
…
Mapped files
Shared, variable size, support on file.
Dynamic libraries
code
Particular case of mapped files.
Code & data library is mapped to be executed.
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data
0x0000..
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Example of a process memory map
0xFFFF..
Process’ stack
Thread 1 stack
Dynamic library B
Share memory zone
Memory mapped file F
Dynamic data (heap)
static data w/o initial value
static data with initial value
code
0x0000..
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Memory
To inspect a process
Disk
P1
O.S.
Details of the sections of a process:
Executable
acaldero@phoenix:~/infodso/$ cat /proc/1/maps
b7688000-b7692000
b7692000-b7693000
b7693000-b7694000
b7694000-b769d000
b769d000-b769e000
b769e000-b769f000
b769f000-b76b2000
b76b2000-b76b3000
b76b3000-b76b4000
b76b4000-b76b6000
..
b78b7000-b78b8000
b78b8000-b78d4000
b78d4000-b78d5000
b78d5000-b78d6000
b78d6000-b78ef000
b78ef000-b78f0000
b78f0000-b78f1000
b81e5000-b8247000
bf851000-bf872000
address
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r-xp
r--p
rw-p
r-xp
r--p
rw-p
r-xp
r--p
rw-p
rw-p
00000000
00009000
0000a000
00000000
00008000
00009000
00000000
00012000
00013000
00000000
08:02
08:02
08:02
08:02
08:02
08:02
08:02
08:02
08:02
00:00
1491
1491
1491
3380
3380
3380
1414
1414
1414
0
/lib/libnss_files-2.12.1.so
/lib/libnss_nis-2.12.1.so
/lib/libnsl-2.12.1.so
r-xp
r-xp
r--p
rw-p
r-xp
r--p
rw-p
rw-p
rw-p
00000000
00000000
0001b000
0001c000
00000000
00019000
0001a000
00000000
00000000
00:00
08:02
08:02
08:02
08:02
08:02
08:02
00:00
00:00
0
811
811
811
1699
1699
1699
0
0
[vdso]
/lib/ld-2.12.1.so
/lib/ld-2.12.1.so
/lib/ld-2.12.1.so
/sbin/init
/sbin/init
/sbin/init
[heap]
[stack]
perm. offset
dev i-node
name
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Exercice
fill the attribute of typical regions
Region
Support
Protection
Shared/Priv.
Size
code
File
RX
Shared
Fixed
…
…
…
…
…
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Overview
1.
Introduction
2.
3.
4.
Memory
P1
Disk
O.S.
Executable
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Example of executable file format
Header
Magic number
0
Offset
Initial PC
…
Sections table
1000
code
Sections
data with initial value
Size
code
1000
4000
data with i.v.
5000
1000
data w/o i.v.
---
…
…
…
Symbol T.
8000
1000
500
5000
data w/o initial value
...
8000
Symbol table
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Memory
Build memory map from exe.
Disk
P1
O.S.
Executable file
0
Executable
Magic number
Initial PC
…
Sections table
1000
code
5000
Memory map
0
code
data with initial val.
data w/o initial val.
4000
5000
data with initial value
data w/o initial value
...
8000
Symbol table
stack
Application arguments
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Memory
Inspect an executable
Disk
P1
O.S.
Executable
Dependences of one executable (dynamic libraries):
acaldero@phoenix:~/infodso/$ ldd main.exe
linux-gate.so.1 => (0xb7797000)
libdinamica.so.1 => not found
libc.so.6 => /lib/libc.so.6 (0xb761c000)
/lib/ld-linux.so.2 (0xb7798000)
Symbols in one executable:
acaldero@phoenix:~/infodso/$ nm main.exe
08049f20 d _DYNAMIC
08049ff4 d _GLOBAL_OFFSET_TABLE_
0804856c R _IO_stdin_used
w _Jv_RegisterClasses
08049f10 d __CTOR_END__
08049f0c d __CTOR_LIST__
...
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Memory
To inspect an executable
Disk
P1
O.S.
Executable
Details of the executable sections:
acaldero@phoenix:~/infodso/$ objdump –x main.exe
...
Program Header:
...
DYNAMIC off
filesz
...
STACK off
filesz
...
Dynamic Section:
NEEDED
NEEDED
INIT
...
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0x00000f20 vaddr 0x08049f20 paddr 0x08049f20 align 2**2
0x000000d0 memsz 0x000000d0 flags rw0x00000000 vaddr 0x00000000 paddr 0x00000000 align 2**2
0x00000000 memsz 0x00000000 flags rw-
libdinamica.so
libc.so.6
0x08048368
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Memory
To inspect an executable
Disk
P1
O.S.
Executable
(contd.)
Sections:
Idx Name
0 .interp
...
12 .text
...
23 .bss
Size
VMA
LMA
File off
00000013 08048134 08048134 00000134
CONTENTS, ALLOC, LOAD, READONLY, DATA
Algn
2**0
0000016c 080483e0 080483e0 000003e0
CONTENTS, ALLOC, LOAD, READONLY, CODE
2**4
00000008
ALLOC
2**2
0804a014
0804a014
00001014
...
SYMBOL TABLE:
08048134 l
d .interp
08048148 l
d .note.ABI-tag
08048168 l
d .note.gnu.build-id
...
0804851a g
F .text 00000000
08048494 g
F .text 00000014
08048368 g
F .init 00000000
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00000000
00000000
00000000
.interp
.note.ABI-tag
.note.gnu.build-id
.hidden __i686.get_pc_thunk.bx
main
_init
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Overview
1.
Introduction
2.
3.
4.
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Virtual memory based systems
1
Virtual
address
2
MMU
3b
3a
Virtual M.
56
Main M.
Secondary M.
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1
Virtual
address
2
MMU
3a
3b
Each application has its own
address space.
Virtual M.
57
Main
M. (and physical)
Secondary
The
virtual
spaceM.
is
divided in block (power of 2), being
this block the allocation unit.
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1
Virtual
address
2
MMU
3b
The MMU (memory management
unit)
3a
will translate the virtual address into
the physical address.
Virtual M.
58
Main M.
Secondary M.
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1
Virtual
address
2
MMU
3b table. It
The O.S. has a translation
3a
translate where each block is located.
There are one table per process.
Virtual M.
Main M.the O.S. has: Secondary M.
Additionally
Frame table (which one is free)
Regions table per process.
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Virtual memory introduction
Virtual M.
60
Main M.
Secondary M.
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…
lw $t0 vector
…
Virtual M.
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Main M.
Secondary M.
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…
lw $t0 vector
…
Virtual M.
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Main M.
Secondary M.
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…
lw $t0 vector
…
Virtual M.
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Main M.
Secondary M.
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Page fault
Virtual M.
Main M.
Secondary M.
The page fault is an exception that executes the associated handler in the O.S.
The handler requests the associated disk blocks, and blocks the process.
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Virtual M.
Main M.
Secondary M.
The disk hardware interruption handler transfers the requested
blocks into main memory, and fire a disk software interruption.
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Virtual M.
Main M.
Secondary M.
The disk software interruption updates the ‘block’ table, and turns the
process’ status into ready for execution.
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Hit
…
lw $t0 vector
…
Virtual M.
Main M.
Secondary M.
It is resumed the execution of the instruction that leads to the page
fault.
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Hit
…
lw $t0 vector+4
…
Virtual M.
Main M.
Secondary M.
The next instruction from the same block will not lead to page fault.
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Summary of
page fault exception
• char buffer[1024];
…
App.
• buffer[1020]=‘\0’;
…
P.F. excep.
• Req. Block
• Go to Pi+1
S.O.
• Copy into RAM
• Fire Soft.Int.
(kernel)
Sw. Int.
Hw. Int.
• Update
table
• Pi ready
HW.
CPU
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Disk
RAM
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Óscar Pérez Alonso y Alejandro Calderón Mateos
Workspace and multiprogramming
Process 1
70
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
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Process 3
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
Process 2
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
Process 1
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
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Process 3
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
Process 2
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
Process 1
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
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Process 3
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
Process 2
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
Process 1
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
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Virtual memory: Windows 7
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Virtual memory: Windows 8.x
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ARCOS @ UC3M
Virtual memory: Linux
76
ARCOS @ UC3M
Windows: perfmon
77
http://technet.microsoft.com/en-us/library/cc958290.aspx
ARCOS @ UC3M
Linux: ps, top, …
arcos:~$ ps -o min_flt,maj_flt 1
MINFL MAJFL
18333
25
Minor fault: it
bookings a page
Major fault: it needs
to access to Disk
78
http://wwwithcyberciti.biz/faq/linux-command-to-see-major-minor-pagefaults/
ARCOS @ UC3M
Linux: ps, top, …
arcos:~$ vmstat 1 5
procs
-----------memory---------- ---swap-- -----io---- -system-- ----cpu----r b
swpd
free
buff
cache
si
so
bi
bo
in
cs us sy id wa
1 0
140 3092132 1575132 2298820
0
0
12
19
20
32 1 2 97 0
0 0
140 3092124 1575132 2298820
0
0
0
0 128 250 0 0 100 0
0 0
140 3092124 1575132 2298820
0
0
0
16 143 281 0 0 100 1
0 0
140 3092124 1575132 2298820
0
0
0
0 137 247 0 0 100 0
0 0
140 3092124 1575132 2298820
0
0
0
0 138 270 0 0 100 0
Procs
r: The number of processes waiting for run time.
b: The number of processes in uninterruptible sleep.
Memory
swpd: the amount of virtual memory used.
free: the amount of idle memory.
buff: the amount of memory used as buffers.
cache: the amount of memory used as cache.
inact: the amount of inactive memory. (-a option)
active: the amount of active memory. (-a option)
Swap
si: Amount of memory swapped in from disk (/s).
so: Amount of memory swapped to disk (/s).
79
IO
bi: Blocks received from a block device (blocks/s).
bo: Blocks sent to a block device (blocks/s).
System
in: The number of interrupts per second, including the clock.
cs: The number of context switches per second.
CPU
These are percentages of total CPU time.
us: Time spent running non-kernel code. (user time, including nice time)
sy: Time spent running kernel code. (system time)
id: Time spent idle. Prior to Linux 2.5.41, this includes IO-wait time.
wa: Time spent waiting for IO. Prior to Linux 2.5.41, included in idle.
st: Time stolen from a virtual machine. Prior to Linux 2.6.11, unknown.
http://wwwithcyberciti.biz/faq/linux-command-to-see-major-minor-pagefaults/
ARCOS @ UC3M
1
Virtual
address
2
MMU
3b
3a
Virtual M.
80
Main M.
Secondary M.
ARCOS @ UC3M
Virtual Memory
Paging
Virtual address
Dirección real
Desplazamiento
N.º pág.
Desplazamiento
N.º marco
Registro
Offset
Puntero a tabla
de páginas
N.º página
Page Table
+
Programa
N.º marco
Mecanismo de paginación
Virtual address
Dirección real
Desplazamiento (d)
N.º seg.
Memoria principal
base + d
+
Programa
Segmentation w. paging
+
Segment Table
long.
d
N.º segmento
Puntero a tabla
de segmentos
base
Mecanismo de segmentación
Virtual address
N
.
º
s
e
g
.
N
.
º
p
a
g
.
segmento
Segmentation
Frame
de
página
Memoria principal
Dirección real
Desplazamiento
N.º marco
Desplazamiento
Programa
81
Mecanismo de
segmentación
+
Mecanismo de
paginación
Frame de
página
Tabla de
página
desp.
Tabla de
segmentos
N.º pág.
+
N.º segmento
Puntero a tabla
de segmentos
Memoria principal
ARCOS @ UC3M
Virtual Memory
Paging
Virtual address
Dirección real
Desplazamiento
N.º pág.
Desplazamiento
N.º marco
Registro
Offset
Puntero a tabla
de páginas
N.º página
Page Table
+
Programa
N.º marco
Virtual address
Dirección real
Desplazamiento (d)
N.º seg.
Memoria principal
base + d
+
Programa
+
Segment Table
long.
d
N.º segmento
Puntero a tabla
de segmentos
base
Virtual address
N
.
º
s
e
g
.
N
.
º
p
a
g
.
segmento
Segmentation
Frame
de
página
Memoria principal
Dirección real
Desplazamiento
N.º marco
Desplazamiento
Programa
82
Mecanismo de
segmentación
+
Mecanismo de
paginación
Frame de
página
Tabla de
página
desp.
Tabla de
segmentos
N.º pág.
+
N.º segmento
Puntero a tabla
de segmentos
Memoria principal
ARCOS @ UC3M
Example
32 bits
011010001001010
22 bits
Virtual address
1111100100000
Physical address
Secondary memory
83
ARCOS @ UC3M
Example
32 bits
011010001001010
22 bits
Virtual address
1111100100000
Physical address
Secondary memory
Divided into equal sized blocks -> pages
84
ARCOS @ UC3M
Example
20 bits
12 bits
Page ID
Offset
Virtual address
22 bits
1111100100000
Physical address
Page ID
85
ARCOS @ UC3M
Example
20 bits
12 bits
Page ID
Offset
Virtual address
10 bits
Frame
12 bits
Offset
Physical address
Frame
Page ID
86
ARCOS @ UC3M
Example
20 bits
12 bits
Page ID
Offset
Virtual address
10 bits
12 bits
Frame
Offset
Physical address
Frame
Page Table
Page ID
Translation from Page ID to Frame -> Page Table
87
ARCOS @ UC3M
Example
20 bits
12 bits
Page ID
Offset
10 bits
Virtual address
12 bits
Frame
Offset
Physical address
Frame
Page Table
Page ID
PM
+ control bits
Frame ID
…
…
Translation from Page ID to Frame -> Page Table
88
ARCOS @ UC3M
Example
20 bits
12 bits
Page ID
Offset
10 bits
Virtual address
12 bits
Frame
Offset
Physical address
Frame
Page Table
09
Page ID
10
10
11
89
1M
+ control bits
Frame ID
…
…
ARCOS @ UC3M
Example
20 bits
12 bits
Page ID
Offset
10 bits
Virtual address
12 bits
Frame
Offset
Physical address
Frame
Page Table
09
Page ID
10
10
0M
11
+ control bits
Frame ID
…
…
Swap space
Secondary memory
90
ARCOS @ UC3M
Virtual Memory
Paging
Virtual address
Dirección real
Desplazamiento
N.º pág.
Desplazamiento
N.º marco
Registro
Offset
Puntero a tabla
de páginas
N.º página
Page Table
+
Programa
N.º marco
Virtual address
Dirección real
Desplazamiento (d)
N.º seg.
Memoria principal
base + d
+
Programa
+
Segment Table
long.
d
N.º segmento
Puntero a tabla
de segmentos
base
Virtual address
N
.
º
s
e
g
.
N
.
º
p
a
g
.
segmento
Segmentation
Frame
de
página
Memoria principal
Dirección real
Desplazamiento
N.º marco
Desplazamiento
Programa
91
Mecanismo de
segmentación
+
Mecanismo de
paginación
Frame de
página
Tabla de
página
desp.
Tabla de
segmentos
N.º pág.
+
N.º segmento
Puntero a tabla
de segmentos
Memoria principal
ARCOS @ UC3M
Example
32 bits
011010001001010
24 bits
Virtual address
1111100100000
Physical address
92
ARCOS @ UC3M
Example
32 bits
011010001001010
24 bits
Virtual address
1111100100000
Physical address
Paging uses fixed sized
regions (pages)
Variable sized regions -> segments
93
ARCOS @ UC3M
Example
16 bits
16 bits
Segment ID
Virtual address
Offset
24 bits
1111100100000
Physical address
94
ARCOS @ UC3M
Example
16 bits
16 bits
Segment ID
Virtual address
Offset
8 bits
Base
16 bits
Offset
Physical address
95
ARCOS @ UC3M
Example
16 bits
16 bits
Segment ID
Offset
Virtual address
8 bits
16 bits
Base
Offset
Physical address
Base
Segment ID
Segment Table
Translation from V.M. to P.M. -> segment table
96
ARCOS @ UC3M
Example
16 bits
16 bits
Segment ID
Offset
Virtual address
8 bits
16 bits
Base
Offset
Physical address
Base
Segment ID
Segment Table
P M + bits
Length
…
Base
…
Translation from V.M. to P.M. -> segment table
97
ARCOS @ UC3M
Example
16 bits
16 bits
Segment ID
Virtual address
Offset
8 bits
16 bits
Base
Offset
Physical address
Base
Segment ID
Segment Table
1 M + bits
…
98
Length
Base
…
ARCOS @ UC3M
Example
16 bits
16 bits
Segment ID
Offset
8 bits
Virtual address
16 bits
Base
Offset
Physical address
Base
Segment ID
Segment Table
0 M + bits
…
Length
Base
…
Swap space
99
ARCOS @ UC3M
Virtual Memory
Paging
Virtual address
Dirección real
Desplazamiento
N.º pág.
Desplazamiento
N.º marco
Registro
Offset
Puntero a tabla
de páginas
N.º página
Page Table
+
Programa
N.º marco
Virtual address
Dirección real
Desplazamiento (d)
N.º seg.
Memoria principal
base + d
+
Programa
+
Segment Table
long.
d
N.º segmento
Puntero a tabla
de segmentos
base
Virtual address
N
.
º
s
e
g
.
N
.
º
p
a
g
.
segmento
Segmentation
Frame
de
página
Memoria principal
Dirección real
Desplazamiento
N.º marco
Desplazamiento
Programa
100
Mecanismo de
segmentación
+
Mecanismo de
paginación
Frame de
página
Tabla de
página
desp.
Tabla de
segmentos
N.º pág.
+
N.º segmento
Puntero a tabla
de segmentos
Memoria principal
ARCOS @ UC3M
Virtual Memory:
segmentation with paging
An entry of the segment table “points to”
a page table associated with the segment.
The variable sized segments are build up from
fixed sized pages.
101
ARCOS @ UC3M
Address translation
Virtual address
Seg.
ID
Pag.
ID
Physical address
Offset
Frame ID
Offset
Process
102
Segmentation
+
Paging
Main Memory
ARCOS @ UC3M
Page frame
Page Table
Page ID
+
Segment ID
Segment Table
offset
Segment table
pointer
Virtual Memory:
An entry of the segment table “points to”
a page table associated with the segment.
The variable sized segments are build up from
fixed sized pages.
inner
Best from both worlds:
Segmentation:
It facilitates memory regions management
It avoids the inner framentation (it has outter one)
Paging:
outter
It optimizes the secondary memory access
It avoids the outter fragmentation (it has inner one)
103
ARCOS @ UC3M
Virtual Memory
summary
Paging
Virtual address
Dirección real
Desplazamiento
N.º pág.
Desplazamiento
N.º marco
Registro
Offset
Puntero a tabla
de páginas
N.º página
Page Table
+
Programa
N.º marco
Virtual address
Dirección real
Desplazamiento (d)
N.º seg.
Memoria principal
base + d
+
Programa
+
Segment Table
long.
d
N.º segmento
Puntero a tabla
de segmentos
base
Virtual address
N
.
º
s
e
g
.
N
.
º
p
a
g
.
segmento
Segmentation
Frame
de
página
Memoria principal
Dirección real
Desplazamiento
N.º marco
Desplazamiento
Programa
104
Mecanismo de
segmentación
+
Mecanismo de
paginación
Frame de
página
Tabla de
página
desp.
Tabla de
segmentos
N.º pág.
+
N.º segmento
Puntero a tabla
de segmentos
Memoria principal
ARCOS @ UC3M
Memory management
advanced aspects
1
Dirección
virtual
2
MMU
3b
3a
M. virtual
M. principal
M. secundaria
TLB
Multi-level tables
105
ARCOS @ UC3M
Translatation cache
Virtual memory based on page tables:
Problem: two access to memory (slow)
To the segment/paging table + to the data/instruction itself
Solution: TLB
Translation cache
TLB (Translation Lookaside Buffer)
Associative Cache Memory that stores the page table entries
most used recently.
It is used to speedup the search stage
106
ARCOS @ UC3M
Address translation (with TLB)
Virtual address
Page ID
Main Memory
Second. Memory
Offset
TLB hit
Offset
Page
loads
Page Table
TLB
Miss
Frame ID
Offset
Physical address
Page fault
107
ARCOS @ UC3M
Multilevel paging
Virtual memory based on page tables:
Problem: amount of memory needed for all tables
E.g.: 4KB pages, 32 bits v. address, and 4 bytes per entry:
220 * 4 = 4MB per process
Solution: multilevel tables
Multi-level table
Two level translation scheme:
The first level page table is always in main memory
Only the second level page tables needed are in main memory
More compact tables: 210 * 4 = 4KB per table
108
ARCOS @ UC3M
Multi-level table
Virtual address
Leve
l
level
2
Physical address
Offset
Frame ID
Offset
Process
109
+
Multilevel paging
Main memory
ARCOS @ UC3M
Page Frame
Page table
(level 2)
Page ID
+
P.T. ID
Page table
(level 1)
offset
P.T. Base
register
ARCOS Group
Universidad Carlos III de Madrid
Lesson 6 (a)
Memory management
Operating System Design
Bachelor in Informatics Engineering

stack - Arcos

Transcription

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