Understanding pool usage using Windows Performance Analyzer

1. HW-927P Understanding pool usage using Windows Performance Analyzer Rahul Nair Program Manager Microsoft Corporation

2. Agenda • Pool Overview and Concepts • Demo: Collecting and Analyzing Pool Data • Guidelines and Best Practices • Key takeaways

3. Pool Overview

4. Pool Overview • Memory resource for kernel mode components that the OS and device drivers use to store their data structures • Primary Audience - Driver Developers • Motivation • Pool usage is a significant contributor to the overall memory usage on a machine • Largest consumer of memory immediately after boot • Any reduction in Pool usage will reduce the overall memory usage of the system across the OS

5. Session Pool NX NonPaged Pool Paged Pool • New for Windows 8: Non Paged Pool allocations which are non-executable Pool Overview NonPaged Pool • The Windows Pool has four basic allocation areas: • Allocations that are guaranteed to reside in memory • Allocations that can be paged out of memory to the pagefile • Allocations made per session. These allocations are pageable

6. Pool Data Collection and Analysis

7. Pool Vocabulary • General • Pool Type –Non Paged Pool, Paged Pool etc. • Session or Non-Session • Basic Data • Lifetime – How long an allocation remains outstanding • Size – Size of an allocation • Stack – Stack corresponding to the allocation • Address – Address corresponding to allocation • Page Address – Page within which the allocation was placed • Metadata • Pool Tag – 4 character label associated with an allocation • Pool Tag Module – Module responsible for allocation • Small Pool – Allocations smaller than a page (<4KB) • Big Pool – Allocations larger than (>=4kB) • NX Bit – Represents non executable allocations • Context: • Transient – allocations with a short lifetime, measured in milliseconds • Outstanding – allocations that remain alive at the point in time being investigated

8. Pool Data Collection • Pool data is collected system wide and not restricted to a single process or driver • Steps • Open Windows performance recorder UI • Select Target application to be “Entire System” • Select Pool Usage from the Memory Profiles • Select scenario of Interest • General or On/Off scenario • Click on ‘Start’ to start tracing and ‘Save’ to save the trace when done WindowsPerformance Recorder UI

9. WPA Pool Analysis • WPA displays 4 graphs for Pool • Pool Cumulative Allocation Size • Whatis the total size of allocations to a particular point in time? • Pool Cumulative Allocation Count • What is the total number of allocations to a particular point in time? • Pool Outstanding Allocation Size • What is size of all allocations alive at a given point in time? • Pool Outstanding Allocation Count • What is the total number of allocations alive at a given point in time? Pool graphs in Windows Performance Analyzer

10. Summary Tables • Raw data is exposed via summary tables • Vocabulary • Allocation lifetime is expressed based on the visible region used to generate the table • AIFO - Allocated inside, freed outside • AIFI - Allocated inside, freed inside • AOFO - Allocated outside, freed outside • AOFI - Allocated outside, freed inside Enable Summary table view Summary table views for Windows Performance Analyzer

11. Demo

12. Guidance/Best Practices

13. Guidance and Best practices • Approach • Understand and optimize pool usage for the most important user scenarios • Transient and steady state memory usage • Guidance • Pool usage • Be judicious and economical in allocation size and count • Minimize Non Paged usage • Pool allocations, MDL allocations, Non Paged Code • Allocation patterns • Ensure that scenario specific allocations are freed as soon as possible • Avoid excessive pre-allocation that you might never use • Avoid intermingling long and short lived allocations which causes fragmentation and increases memory usage • Move Non Paged allocations to the more secure Non-Executable Non Paged Pool

14. Key Takeaways • Pool usage is a significant contributor to the overall memory usage of a system • Understand the pool usage of your component and utilize the tools to identify areas for optimization

15. For more information RELATED SESSIONS • HW-59T Improving performance with the Windows Performance Toolkit • HW-141T Reducing the memory footprint of drivers and apps • 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

16. thank you Feedback and questions http://forums.dev.windows.com Session feedbackhttp://bldw.in/SessionFeedback

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