4ef0171bc0
This commit introduces a comprehensive tracing mechanism for allocation failures within the Adaptive Cache Engine (ACE) component. This feature allows for precise identification of the root cause for Out-Of-Memory (OOM) issues related to ACE allocations. Key changes include: - **ACE Tracing Implementation**: - Added environment variable to enable/disable detailed logging of allocation failures. - Instrumented , , and to distinguish between "Threshold" (size class mismatch), "Exhaustion" (pool depletion), and "MapFail" (OS memory allocation failure). - **Build System Fixes**: - Corrected to ensure is properly linked into , resolving an error. - **LD_PRELOAD Wrapper Adjustments**: - Investigated and understood the wrapper's behavior under , particularly its interaction with and checks. - Enabled debugging flags for environment to prevent unintended fallbacks to 's for non-tiny allocations, allowing comprehensive testing of the allocator. - **Debugging & Verification**: - Introduced temporary verbose logging to pinpoint execution flow issues within interception and routing. These temporary logs have been removed. - Created to facilitate testing of the tracing features. This feature will significantly aid in diagnosing and resolving allocation-related OOM issues in by providing clear insights into the failure pathways.
195 lines
6.7 KiB
Markdown
195 lines
6.7 KiB
Markdown
# Phase 8 - Executive Summary
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**Date**: 2025-11-30
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**Status**: COMPLETE
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**Next Phase**: Phase 9 - SuperSlab Deep Dive (CRITICAL PRIORITY)
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## What We Did
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Executed comprehensive benchmarks comparing HAKMEM (Phase 8) against System malloc and mimalloc:
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- 30 benchmark runs total (3 allocators × 2 working sets × 5 runs each)
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- Statistical analysis with mean, standard deviation, min/max
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- Root cause analysis from debug logs
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- Detailed technical reports generated
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## Key Findings
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### Performance Results
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| Benchmark | HAKMEM | System | mimalloc | Gap vs System | Gap vs mimalloc |
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|-------------------|--------|--------|----------|---------------|-----------------|
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| WS256 (Hot Cache) | 79.2 | 86.7 | 114.9 | -9.4% | -45.2% |
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| WS8192 (Realistic)| 16.5 | 57.1 | 96.5 | -246% | -485% |
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*All values in M ops/s (millions of operations per second)*
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### Critical Issues Identified
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1. **SuperSlab Scaling Failure** (SEVERITY: CRITICAL)
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- HAKMEM degrades 4.80x from hot cache to realistic workload
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- System malloc degrades only 1.52x
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- mimalloc degrades only 1.19x
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- **Root cause**: SuperSlab architecture doesn't scale
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- **Evidence**: "shared_fail→legacy" messages in logs
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2. **Fast Path Overhead** (SEVERITY: MEDIUM)
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- Even with hot cache, HAKMEM is 9.4% slower than System malloc
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- **Root cause**: TLS drain overhead, SuperSlab lookup costs
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3. **Competitive Position** (SEVERITY: CRITICAL)
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- At realistic workloads, HAKMEM is 3.46x slower than System malloc
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- mimalloc is 5.85x faster than HAKMEM
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- **Conclusion**: HAKMEM is not production-ready
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## What This Means
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### The Good
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- Benchmarking infrastructure works perfectly
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- Statistical methodology is sound (low variance, reproducible)
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- We have clear diagnostic data and debug logs
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- We know exactly what's broken
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### The Bad
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- SuperSlab architecture has fundamental scalability issues
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- Performance gap is too large to fix with incremental optimizations
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- 246% slower than System malloc at realistic workloads is unacceptable
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### The Ugly
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- May need architectural redesign (Hybrid approach or complete rewrite)
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- Current SuperSlab work may need to be abandoned
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- Timeline to production-ready could extend by 4-8 weeks
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## Recommendations
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### Immediate Next Steps (Phase 9 - 2 weeks)
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**Week 1: Investigation**
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- Add comprehensive profiling (cache misses, TLB misses)
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- Analyze "shared_fail→legacy" root cause
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- Measure SuperSlab fragmentation
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- Benchmark different SuperSlab sizes (1MB, 2MB, 4MB)
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**Week 2: Targeted Fixes**
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- Implement hash table for SuperSlab lookup
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- Fix shared slab capacity issues
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- Optimize fast path (more inlining, fewer branches)
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- Test larger SuperSlab sizes
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**Success Criteria**:
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- Minimum: WS8192 improves from 16.5 → 35 M ops/s (2x improvement)
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- Stretch: WS8192 reaches 45 M ops/s (80% of System malloc)
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### Decision Point (End of Phase 9)
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**If successful (>35 M ops/s at WS8192)**:
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- Continue with SuperSlab optimizations
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- Path to production-ready: 6-8 weeks
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- Confidence: Medium (60%)
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**If unsuccessful (<30 M ops/s at WS8192)**:
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- Switch to Hybrid Architecture
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- Keep: TLS fast path layer (working well)
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- Replace: SuperSlab backend with proven design
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- Path to production-ready: 8-10 weeks
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- Confidence: High (75%)
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## Deliverables
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All benchmark data and analysis available in:
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1. **PHASE8_QUICK_REFERENCE.md** - TL;DR for developers (START HERE)
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2. **PHASE8_VISUAL_SUMMARY.md** - Charts and decision matrix
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3. **PHASE8_TECHNICAL_ANALYSIS.md** - Deep dive into root causes
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4. **PHASE8_COMPREHENSIVE_BENCHMARK_REPORT.md** - Full statistical report
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5. **phase8_comprehensive_benchmark_results.txt** - Raw benchmark output (222 lines)
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## Risk Assessment
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### Technical Risks
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- **HIGH**: SuperSlab architecture may be fundamentally flawed
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- **MEDIUM**: Fixes may provide only incremental improvements
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- **LOW**: Benchmarking methodology (methodology is solid)
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### Schedule Risks
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- **HIGH**: May need architectural redesign (adds 3-4 weeks)
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- **MEDIUM**: Phase 9 investigation could reveal deeper issues
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- **LOW**: Tooling and infrastructure (all working well)
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### Mitigation Strategies
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- Have Hybrid Architecture plan ready as fallback (Option B)
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- Set clear success criteria for Phase 9 (measurable, time-boxed)
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- Don't over-invest in SuperSlab if early results are negative
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## Competitive Landscape
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```
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Production Allocators (Benchmark: WS8192):
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1. mimalloc: 96.5 M ops/s [TIER 1 - Best in class]
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2. System malloc: 57.1 M ops/s [TIER 1 - Production ready]
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Experimental Allocators:
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3. HAKMEM: 16.5 M ops/s [TIER 3 - Research/development]
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```
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**Target for Production**: 45-50 M ops/s (80% of System malloc)
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## Budget and Timeline
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### Best Case (Phase 9 successful)
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- Phase 9: 2 weeks (investigation + fixes)
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- Phase 10-12: 4 weeks (optimizations)
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- **Total**: 6 weeks to production-ready
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- **Cost**: Low (mostly optimization work)
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### Likely Case (Hybrid Architecture)
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- Phase 9: 2 weeks (investigation reveals need for redesign)
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- Phase 10: 1 week (planning Hybrid approach)
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- Phase 11-13: 4 weeks (implementation)
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- Phase 14: 1 week (validation)
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- **Total**: 8 weeks to production-ready
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- **Cost**: Medium (partial rewrite of backend)
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### Worst Case (Complete rewrite)
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- Phase 9: 2 weeks (investigation)
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- Phase 10: 2 weeks (architecture design)
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- Phase 11-15: 8 weeks (implementation)
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- **Total**: 12 weeks to production-ready
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- **Cost**: High (throw away SuperSlab work)
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**Recommended**: Plan for Likely Case (8 weeks), prepare for Worst Case
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## Success Metrics
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### Phase 9 Targets (2 weeks from now)
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- [ ] WS256: 79.2 → 85+ M ops/s
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- [ ] WS8192: 16.5 → 35+ M ops/s
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- [ ] Degradation: 4.80x → 2.50x
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- [ ] Zero "shared_fail→legacy" events
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- [ ] Understand root cause of scalability issue
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### Phase 12 Targets (6-8 weeks from now)
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- [ ] WS256: 90+ M ops/s (match System malloc)
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- [ ] WS8192: 45+ M ops/s (80% of System malloc)
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- [ ] Degradation: <2.0x (competitive with System malloc)
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- [ ] Production-ready: passes all stress tests
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## Conclusion
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Phase 8 benchmarking successfully identified critical performance issues with HAKMEM. The data is statistically robust, reproducible, and provides clear direction for Phase 9.
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**Bottom Line**:
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- SuperSlab architecture is broken at scale
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- We have 2 weeks to fix it (Phase 9)
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- If unfixable, we have a viable fallback plan (Hybrid Architecture)
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- Timeline to production-ready: 6-10 weeks depending on Phase 9 results
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**Recommendation**: Proceed with Phase 9 investigation IMMEDIATELY. This is the critical path to success.
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---
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**Prepared by**: Claude (Benchmark Automation)
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**Reviewed by**: [Your review]
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**Approved for Phase 9**: [Pending]
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**Questions?** See PHASE8_QUICK_REFERENCE.md or PHASE8_VISUAL_SUMMARY.md for details.
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