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name: profiling-memory-allocations description: Experimental allocation profiler tracking memory allocations at guest-language level. Shows allocation sites, object types, and memory pressure patterns. Use to identify allocation-heavy locations, find unnecessary object creation, and understand memory behavior. High allocations in hot loops = optimization opportunity if escape analysis isn't eliminating them.

Profiling Memory Allocations

Experimental allocation profiler tracking memory allocations at the guest-language level. Identifies allocation-heavy locations and unnecessary object creation.

When to Use This Skill

• Identify allocation-heavy locations in hot loops
• Find unnecessary object creation
• Understand memory behavior patterns
• Detect escape analysis opportunities

Note: High allocations in hot loops = optimization opportunity if escape analysis isn't eliminating them.

Quick Start

Copy# Basic memory tracing
<launcher> --memtracer <program>

# With stack traces
<launcher> --memtracer --memtracer.TraceStackTraces=true <program>

# Filter by allocation count
<launcher> --memtracer --memtracer.TraceMem=1000 <program>

⚠️ REQUIRED: Fermi Verification (Every Tool Invocation)

Before running:

• Pre-calculate: Expected allocation count (estimate based on loops/iterations)
• Smoke test: <launcher> --memtracer -c 'var a = 👉1, 2, 3👈;' → Verify shows allocations

After running:

• Validate: Actual vs estimate within 1 order of magnitude? YES / NO
• If NO: STOP - Debug tool before proceeding (test with known allocating code)
• Save output: tool-outputs/memtracer-[benchmark].txt

Gate: All boxes checked? → Proceed to analysis

Key Options

Understanding Output

Sample Output

CopyMemory Tracer. Recorded 45678 allocations.

Source Location           || Count   || Size      || Type
queens.lox:42            || 50000   || 400KB     || LoxArray
queens.lox:55            || 25000   || 200KB     || LoxObject

Interpretation

Allocation Patterns

High Allocation Sites

If hot loop shows many allocations:

1. Check if objects escape the loop
2. Verify escape analysis is running
3. Consider restructuring to avoid allocation

Common Issues

Issue 1: Array Allocations in Loop

Copyqueens.lox:42  || 50000 allocations

Cause: Creating arrays inside hot loop Fix: Reuse arrays, or ensure they're eliminated by EA

Issue 2: Object Allocations for Temporaries

CopyPoint creation || 100000 allocations

Cause: Temporary objects not eliminated Fix: Keep objects local, avoid escaping references

Integration with Other Skills

Related Skills

• profiling-with-cpu-sampler - Time-based profiling
• analyzing-compiler-graphs - Check escape analysis
• detecting-performance-warnings - Find barriers
• establishing-benchmark-baseline - Set expectations

Reference

Copy<launcher> --help:memtracer