1. Reducing the memory footprint of drivers and apps
9/19/2018 6:26 AM
HW-141T
Reducing the memory footprint of drivers and apps
Rahul Nair
Program Manager
Joe Laughlin
Principal Software Developer
Microsoft Corporation
© 2010 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

2. Agenda You’ll leave with Platform approach to reducing memory usage
Understanding memory usage
Classification of memory types
Using Windows Performance Analyzer
Guidelines and best practices
You’ll leave with
How to understand the memory impact of an app/driver
How to identify areas of opportunity for optimizing memory usage

3. Memory is a key resource, and optimizing memory usage ensures a consistent and responsive user experience.

4. Why is memory important?
Being leaner and more efficient in terms of memory footprint
Ensures a responsive and smooth app experience
Shapes user perception regarding resource utilization
Improves scalability across a range of hardware platforms
Reduces power consumption

5. Platform approach to
Reducing Memory Usage

6. Optimizing memory footprint
Multi-pronged strategy:
Windows
Partners and Ecosystem
Reductions in idle memory usage
Telemetry to help identify opportunities
Platform investments that improve general memory usage
Memory analysis tools
Targeted optimizations for key user scenarios
Education and outreach
Telemetry to help identify additional OS opportunities

7. Understanding
memory usage
Key Concepts

8. Key concepts App cost in totality Impact to system responsiveness
Short term vs. long term impact
Allocation patterns

9. Memory usage of an app/driver
App cost in totality
Memory usage of an app/driver
Holistic view of memory usage
Dimensions
Direct usage
Files
Allocations
Breadth of impact
Frequency of use
Indirect usage
System memory resources
Subsystems
Targeted platform and audience

10. Composition of physical memory
In Use
Available
Process working sets
Critical for system responsiveness
Standby Cache
Non Paged Memory
Free
Modified
Composition of Physical Memory

11. Windows memory management
Available
In Use
Close /Unmap File
Standby Cache
FIFO
Soft Fault
Repurposed
Working Sets
Modify
Modified
Allocation
Hard Fault
Disk
De-allocation
Free
FIFO

12. System responsiveness and the Standby Cache
Standby Cache holds contents that were recently accessed by apps and is critical for ensuring system responsiveness
Enables more efficient utilization of physical memory
Cost of accessing memory from RAM is much lower than the cost of a Disk IO
Important Considerations:
The higher your persistent memory usage  Lesser the availability of RAM for other purposes
Large transient usage can push out more valuable contents

13. Short term vs. long term impact
Understand the memory usage of your Scenario/Component in terms of
Transient or Peak Impact
Persistent or Steady-state Impact
Important considerations
Frequency of peaks will have significant impact on standby cache
Focus on memory usage associated with common user scenarios
Peak
Steady-state
Time
Memory Usage

14. Example: peak vs. steady state
Why is the steady state memory usage growing for this scenario?
Why is there a transient peak in memory usage for this part of the scenario?

15. Allocation Patterns Ideal Fragmentation Fragmentation
Steady state
Peaks
Ideal
Steady state
Peaks
Fragmentation
Fragmentation
Occurs when unused ‘gaps’ arise between blocks of allocated memory
You can no longer allocate a block of memory as big as the available free memory
Due to mixing allocations of longer lifetimes with shorter lifetimes
Important considerations
Focus on grouping together allocations of similar lifetime and size to minimize fragmentation

16. Classification of Memory
Types

17. Basic memory classification
Dynamic
File
High Level Classification
Heap
VirtualAlloc
Paged Pool
Non Paged Pool
Non Paged Driver code
Executables (exe, dll)
Data files (txt, db)
Driver Images (.sys)
Examples
Pageable
Non-Pageable

18. Dynamic user mode allocations
The Windows heap is a memory pool created at start-up that processes use to dynamically allocate memory as needed
Windows heap has three basic dynamic allocation areas:
Services allocations of all sizes, until allocation thresholds are reached
Mainline
(NT Heap)
Composed of sub-segments that service allocations of fixed size once allocation thresholds are met
Low Fragmentation Heap (LFH)
Allocations above 512KB/1MB are allocated using VirtualAlloc
VirtualAlloc

19. Dynamic kernel mode allocations
Pool is the kernel mode equivalent of heap
Memory resource that the OS and device drivers use to store their data structures
The Windows Pool has four basic allocation areas:
Allocations that can be paged out of memory to the pagefile
Paged Pool
Allocations that are guaranteed to reside in physical memory
NonPaged Pool
New for Windows 8: Non executable pages used for these allocations
NX NonPaged Pool
Allocations that are associated to a particular user session
Session Pool

20. Memory data
Windows Performance Analyzer presents data in the form of graphs and summary tables
Memory data:
Basic data
Size - How much?
Lifetime - How long?
Allocation stack - By who?
Address - Where?
Metadata
Based on Memory Type
Example
Heap Handle
Pool Type
Pool tag
Context
Transient - Short lived
Outstanding - Alive at a given point in time

21. Collecting and analyzing memory data
9/19/2018 6:26 AM
demo
Collecting and analyzing memory data
© 2010 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

22. Guidelines and Best
Practices

23. General philosophy Understand peaks and steady state Questions
What do you need long term for normal usage?
What is scenario specific?
Considerations
Minimize steady state
Optimize for your most frequent and most important user scenarios
Manage memory allocations efficiently
Questions
When do you need to allocate memory?
When do you release memory?
Considerations
Be lazy in allocating and diligent in releasing
Avoid excessive pre-allocation that you might never use
Understand allocation patterns
Questions
How frequently do you access a particular allocation?
Would your patterns result in fragmentation?
Considerations
Group together allocations with similar lifetime
Reuse temporary allocations
Avoid frequent allocation/deallocation
Use the Windows Performance Analyzer to analyze and identify areas of optimization

24. Best practices for Driver Developers
Optimizing memory footprint
Understand pool usage
Focus on the most frequent usage and important scenarios like System Boot
Best practices
Focus on non-paged memory usage
Avoid excessive pre-allocation that you might never use
Layout data structures efficiently and reuse them when possible
Avoid mixing long lived allocations with short lived ones which can cause fragmentation
Test and validate to eliminate memory leaks
Move non-paged allocations to the more secure non-executable non-paged pool

25. Best practices for app developers
Optimizing memory footprint
Understand your dynamic memory usage
Focus on the most frequent and important user scenarios
Understand the new Metro style app model and implications
Best practices
Defer memory allocations until you need to use them, especially during app launch
Ensure that scenario specific allocations are freed as soon as possible
Reuse dynamic allocations/temporary buffers whenever possible
Avoid frequent mapping and unmapping of Virtual Address space
Avoid mixing long lived allocations with short lived ones which can cause fragmentation

26. Key takeaways
Memory is a shared resource and good citizenship is important
Has a direct impact on system responsiveness
Approach to reducing memory usage should include
Optimizing for long term and short term impact
Efficiently managing memory allocations
Optimal allocation patterns
Use the tools to actively invest in improving your memory usage

27. Q&A

28. For more information Related sessions Documentation & articles
HW-59T Improving performance with the Windows Performance Toolkit
HW-927P Understanding pool usage using Windows Performance Analyzer
HW-928P Understanding heap data Using Windows Performance Analyzer
HW-977P Understanding VirtualAlloc usage using Windows Performance Analyzer
HW-925P Customizing WPA Trace Views
HW-926P Introduction to the new WPA user interface
Driver Development Tools
Windows Hardware Dev Center
Windows Dev Center

29. thank you Feedback and questions http://forums.dev.windows.com
Session feedback

30. 9/19/2018 6:26 AM
© 2011 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.
© 2011 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.