Virtual and Physical Memory Addressses.

NTDEV
1

Hi everyone,

It is a common practice to use the phyical memory address of a virtual
memory address when developing device drivers.

What happens when the virtual memory gets stored on disk? What ill affects
can we see? How do we remedy it?

Joe McCloskey
Gamry Instruments
xxxxx@gamry.com

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2

If ‘stored on disk’ is interpreted as paged out, then nothing will happen.
Except that when you touch that page again it will be paged back in. If you
have a PA on the VA, then you got it by some means which required you to
lock the pages in memory, hence they will never be paged out.

Pete

Peter Scott
xxxxx@KernelDrivers.com
http://www.KernelDrivers.com

-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com]On Behalf Of
xxxxx@gamry.com
Sent: Friday, September 21, 2001 1:15 PM
To: NT Developers Interest List
Subject: [ntdev] Virtual and Physical Memory Addressses.

Hi everyone,

It is a common practice to use the phyical memory address of a virtual
memory address when developing device drivers.

What happens when the virtual memory gets stored on disk? What ill affects
can we see? How do we remedy it?

Joe McCloskey
Gamry Instruments
xxxxx@gamry.com

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3

> It is a common practice to use the phyical memory address of a virtual

memory address when developing device drivers.

No, according to MS’s ideas, you will need the physical address for DMA
only.
Drivers usually use MDLs which describe both physical and virtual addresses.

What happens when the virtual memory gets stored on disk?

You can use the physical addresses of the buffer only while it is locked in
the memory.

Max

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