Using Virtual Memory in your application

Using Virtual Memory in
your application

Introduce to Windows Memory
Management
• Windows 了 理
• Virtual Memory
• 理 列 列
• Memory-Mapped Mapped File
• 料 串 流 ()) , 料
• Heap
• 理 量 料
• Virtual Memory
1
Reserving
• 留
2 3
Commit
Read/Write

Win32 理
料 來 : ms-help://MS.MSDNQTR.2004JAN.1033/dngenlib/html/msdn_virtmm.htm

Reserving a Region in an Address Space
NULL
bytes
bytes
(
(
Page
Page
size
size
數 )
)
Reserving
MEM_COMMIT
MEM_COMMIT
MEM_RESERVE
MEM_RESERVE
留
;
;
PAGE_READWRITE
PAGE_READWRITE
• 列 , VirtualAlloc NULL ((
)
•
• 不 user-mode partition
Windows 2000 user-mode partition : 0x00010000-0x7FFEFFFF
Windows 98 user-mode partition : 0x00400000-0x7FFFFFFF

Reserving
PVOID buffer=VirtualAlloc((LPVOID)0x003c0000,
64*1024,MEM_RESERVE, PAGE_READWRITE);
if(buffer==NULL)
ShowError();
return 0;
(bytes) (bytes)
Reserving
Reserving
, 不
, 0x003c0000
不
讀
0x00010000-0x7FFEFFFF ,

?
• VirtualQuery

來 例
void main(){
// Step 1: 0x003c0000 狀
ShowMemoryStatus((LPVOID)0x003c0000);
}
PVOID buffer=VirtualAlloc((LPVOID)0x003c0000,
64*1024,MEM_RESERVE,
PAGE_READWRITE);
if(buffer==NULL)
ShowError();
// Step 2: 0x003c0000+ page 狀
ShowMemoryStatus((LPVOID)(0x003c0000+4*1024));

料 來
VirtualQuery

COMMIT
• 若 ,
• Reserving , COMMIT
PVOID buffer=VirtualAlloc((LPVOID)0x003c0000,
64*1024,MEM_COMMIT, PAGE_READWRITE);
if(buffer==NULL)
ShowError();
return 0;
PVOID buffer=VirtualAlloc((LPVOID)0x003c0000, 1 reserve reserve
64*1024,MEM_RESERVE, PAGE_READWRITE);
buffer=VirtualAlloc((LPVOID)0x003c0000,
64*1024,MEM_COMMIT, PAGE_READWRITE);
if(buffer==NULL)
ShowError();
return 0;
2 commit commit
, 不
, 不 了

論
• , VirtualAlloc 來
• granularity boundary (64KB)
1
void main(){
64 KB 說
300 300 ** 64 64 K + 8192 8192
PVOID buffer=VirtualAlloc((LPVOID)(300 * 65536+8192),
64*1024,MEM_RESERVE,
PAGE_READWRITE);
if(buffer==NULL)
ShowError();
}
2
300 300 ** 64 64 K
(8192 (8192 ) )

Reserve 略
• 留 ,
.
void main(){
料
}
PVOID buffer=VirtualAlloc(NULL,
98 98 不
64*1024,MEM_RESERVE | MEM_TOP_DOWN ,
PAGE_READWRITE);

•
Protected
• PAGE_NOACCESS, PAGE_READWRITE,
PAGE_READONLY,
• PAGE_ EXECUTE, , PAGE_EXECUTE
EXECUTE_READ,
PAGE_EXECUTE
EXECUTE_READWRITE
98 98 不
Windows 98
PAGE_ EXECUTE, PAGE_EXECUTE_READ PAGE_READONLY
PAGE_EXECUTE_READWRITE PAGE_READWRITE

Committing
Reserve
•
Commit , 行
• page file
Reserve
void main(){
}
•
page (4 KB)
Step Step 1: 1: Reserving Reserving
PVOID buffer=VirtualAlloc(NULL,
64*1024,MEM_RESERVE, PAGE_READWRITE);
buffer=VirtualAlloc(buffer,
4*1024,MEM_COMMIT, PAGE_READWRITE);
,page
page page commit
Step Step 2: 2:

例
void main(){
// Step 1: Reserve 64 KB
PVOID buffer=VirtualAlloc(NULL, 64*1024,MEM_RESERVE,PAGE_READWRITE);
if(buffer==NULL)
ShowError();
// Step 2: , 1 page
buffer=VirtualAlloc(buffer, 4*1024,MEM_COMMIT,PAGE_READWRITE);
if(buffer==NULL)
ShowError();
Page protected
PAGE_READONLY
// Step 3: 例
for(int i=0;i

• 若 5,242,880
5,242,880
Reserve
512 kB , commit
5,242,880 + 2k 6KB
5,242,880+2k
512k
5,242,880
6KB
Commit Commit
VirtualAlloc((PVOID) (5242880 + (2 * 1024)), 6 * 1024,
MEM_COMMIT, PAGE_READWRITE);
page page
4KB 4KB
4KB 4KB
5,242,880 ~ 5,242,880 + 8k-1
8 kB
page page 數

1. Reserve
2. 行 Commit
不 ?
理 !! !!
VirtualAlloc((PVOID) (NULL, 99 * 1024,
MEM_RESERVE| MEM_COMMIT, PAGE_READWRITE);
100 kB
Why ?
page size(4KB) 數
: 若 不 , NULL

COMMIT
•
128 bytes
CELLDATA CellData[200][256];
128 128 * 200 200 * 256 256 = 6,553,600 = 64 64 KB KB
數 ,
數 ,
浪

Virtual Memory
• Reserving , 不
•
料 ,
COMMIT Cell
什 不 linked
list 料 ?
linked list 理 料 ,
料

Commit
Exception,
略 Exception ,
Commit

state Free 狀
VirtualFree( , 0 , MEM_RELEASE )
state Reserve 狀
VirtualFree( , , MEM_DECOMMIT )
page page

行 ,
更 protected
…
什 ?
Debug 便
類 來 理 料
1. 理 : memory PAGE_READWRITE
2. 離 類 :
memory PAGE_READONLY
來 ,, ,
Exception.

例
void main(){
// Step 1: Reserve & COMMIT 64 KB
PVOID buffer=VirtualAlloc(NULL, 64*1024,MEM_RESERVE | \
MEM_COMMIT,PAGE_READWRITE);
if(buffer==NULL)
ShowError();
// Step 2:
for(int i=0;i

Memory Reset
• , RAM 行 .
• Page fault:
page 不 RAM
, page file 料
page RAM
RAM.
page
RAM

RAM 不
• RAM
(page),
page file .
• Page 料
• 料 更
file .
RAM page page file
料
page page
料 不 ,
了
Memory Reset

• 料
• , 料 不 了
• Free ,
來 ,
不 care 料 了 .

int _tmain(int argc, _TCHAR* argv[]) {
// Step 1: Reserve & COMMIT 64 KB
PVOID buffer=VirtualAlloc(NULL, 64*1024,MEM_RESERVE |
MEM_COMMIT,PAGE_READWRITE);
if(buffer==NULL) ShowError();
// Step 2:
for(int i=0;i

PINT pnData = (PINT) VirtualAlloc(NULL, 1024, MEM_RESERVE | MEM_COMMIT, \
PAGE_READWRITE);
pn[0] = 100;
pn[1] = 200;
VirtualAlloc((PVOID) pnData, sizeof(int), MEM_RESET, PAGE_READWRITE);
pnData 4 bytes Reset
MEM_RESET ,
RESET page (4KB)
,
,
4092 bytes 料 lose

不 便 亂
VirtualAlloc((PVOID) pnData, 5000, MEM_RESET, PAGE_READWRITE);
RESET ,
VirtualQuery
RegionSize,
RESET
Reset
MEMORY_BASIC_INFORMATION mbi;
VirtualQuery (pszData, &mbi, sizeof(mbi));
VirtualAlloc(pszData, mbi.RegionSize, MEM_RESET, PAGE_READWRITE);
Region Size

End

錄
Global Local functions
• 來 porting 16-bit
, 了
, heap functions
• Windows global local heap
• GlobalAlloc = LocalAlloc
• near far pointer
16- bits Windows
• 16-bit
segmented memory model near/ far pointers
• 32- bit virtual memory model 律 32-bit
• GlobalAlloc LocalAlloc 律 32-bit virtual address
GlobalAlloc/ LocalAlloc heap bytes ,
functions, .

• GlobalAlloc / LocalAlloc
• private, committed pages with read/write access
不 process
process process file-map . .

Copy-On
On-Write
• Windows
, 兩
processes
• 若 10 Notepad 行 , code data
physical memory .
• 行
• instance ,
.

Copy-On
On-Write
• OS 了
例 : : .data .data section section
• .exe .dll
memory ,
page 數 量 , copy-on
on-write
thread thread
RAM RAM free free page page
page page
free free page page
更 page page table table
virtual virtual address address page page

更
Physical Physical memory memory
Virtual Virtual Memory Memory
instances , RAM RAM code
data data map map process virtual virtual space space
executable
executable
image
image
料 ,
,
兩 instances
instances

instance 更 shared
shared 料
Copy-on-Write
Copy-on-Write
instance
instance
page
page
table
table
page
page
instance
instance
來 page
page
• 來 , Process 1 更
global/static 數 , 不