net garbage collection performance tips
DESCRIPTION
In this presentation we review the basics of how the .NET garbage collector operates, and then tackle some best practices that can make the performance of your CLR-based applications improve considerably. For example, we look at garbage collection flavors (server GC, background GC, and others), large object allocations, and finalization. We also review ways to track object allocations and even resolve memory leaks using the PerfView tool.TRANSCRIPT
Sasha Goldshtein
CTOSela Group
@goldshtnblog.sashag.net
Garbage Collection Performance Tips
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GARBAGE COLLECTION PERFORMANCE TIPS
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WHY THIS TALK?
The .NET GC is a complex beast Many performance optimizations over the
years Still many ways to shoot yourself in the foot
Mark and Sweep Generations LOH
Fragmentation Hoarding Segments
Finalization Background GC
VMMap PerfView Server GC
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REFRESHER: TRACING GC
.NET GC is not based on reference counting
GC starts from roots and marks reachable objects as “live”
The rest of the heap is swept as garbage
Usually holes are compacted and objects are moved around
Allocations are very cheap
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PROBLEMS?
Naïve implementation blocks mutators Result: very long application pauses
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GC FLAVORS
CLR 2.0
Workstation GC• Concurrent, non-
concurrent
Server GC• Parallel GC
CLR 4.0
Background workstation GC
CLR 4.5
Concurrent and background server GC
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GENERATIONS
Full GC is slow and very inefficient – most objects are live
New objects die quickly, old objects die hard
Divide the heap into regions, enabling partial collections
Tricky to deal with cross-generation references
Special area for large objects (>85K)
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MEASUREMENT
Profile apps for allocations, not just time Look for large allocations, long-lived objs
Pool temporary large objects
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GC AND VIRTUAL MEMORY
Windows VirtualAlloc has 64KB granularity in user-mode
CLR allocates consecutive 16MB-64MB segments (x86) of memory
On x86, easy to fragment the address space
VMMap to detect, x64/VM hoarding to fix
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FINALIZATION
Finalizer (cleanup) runs automatically after object becomes unreachable
Performance problems and bugs: Allocation/finalization rate
Race conditions, deadlocks
The finalizer may run while a method is still executing on an instance
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CONCLUSIONS
Minimize the number and size of allocations
Strive to quickly kill temporary objects Pool temporary large objects Don’t use finalization. Just don’t
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GARBAGE COLLECTION PERFORMANCE TIPS
ADDITIONAL REFERENCES
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THANK YOU!
Sasha Goldshtein@goldshtn