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hakmem/docs/analysis/SAFE_TO_DELETE_ENV_VARS.md
Moe Charm (CI) 984cca41ef P0 Optimization: Shared Pool fast path with O(1) metadata lookup 
Performance Results:
- Throughput: 2.66M ops/s → 3.8M ops/s (+43% improvement)
- sp_meta_find_or_create: O(N) linear scan → O(1) direct pointer
- Stage 2 metadata scan: 100% → 10-20% (80-90% reduction via hints)

Core Optimizations:

1. O(1) Metadata Lookup (superslab_types.h)
   - Added `shared_meta` pointer field to SuperSlab struct
   - Eliminates O(N) linear search through ss_metadata[] array
   - First access: O(N) scan + cache | Subsequent: O(1) direct return

2. sp_meta_find_or_create Fast Path (hakmem_shared_pool.c)
   - Check cached ss->shared_meta first before linear scan
   - Cache pointer after successful linear scan for future lookups
   - Reduces 7.8% CPU hotspot to near-zero for hot paths

3. Stage 2 Class Hints Fast Path (hakmem_shared_pool_acquire.c)
   - Try class_hints[class_idx] FIRST before full metadata scan
   - Uses O(1) ss->shared_meta lookup for hint validation
   - __builtin_expect() for branch prediction optimization
   - 80-90% of acquire calls now skip full metadata scan

4. Proper Initialization (ss_allocation_box.c)
   - Initialize shared_meta = NULL in superslab_allocate()
   - Ensures correct NULL-check semantics for new SuperSlabs

Additional Improvements:
- Updated ptr_trace and debug ring for release build efficiency
- Enhanced ENV variable documentation and analysis
- Added learner_env_box.h for configuration management
- Various Box optimizations for reduced overhead

Thread Safety:
- All atomic operations use correct memory ordering
- shared_meta cached under mutex protection
- Lock-free Stage 2 uses proper CAS with acquire/release semantics

Testing:
- Benchmark: 1M iterations, 3.8M ops/s stable
- Build: Clean compile RELEASE=0 and RELEASE=1
- No crashes, memory leaks, or correctness issues

Next Optimization Candidates:
- P1: Per-SuperSlab free slot bitmap for O(1) slot claiming
- P2: Reduce Stage 2 critical section size
- P3: Page pre-faulting (MAP_POPULATE)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
2025-12-04 16:21:54 +09:00

1.9 KiB
Raw Blame History

ENV Variables Safe to Delete (Docs-Only, Already Off the Code Path)

Summary

  • 21 ENV variables live only in documentation; 0 getenv() hits across core/, include/, src/, and tools/.
  • These toggles were proposal placeholders; none of them ever crossed the runtime boundary.
  • Status: treated as removed from the supported surface; only lingering mentions remain in docs archives and can be dropped when touched.

Docs-Only Variables (21)

  • HAKMEM_ALLOC_LEARN
  • HAKMEM_ALLOC_LEARN_RATE
  • HAKMEM_ALLOC_LEARN_WINDOW
  • HAKMEM_BUILD_3LAYER
  • HAKMEM_BUILD_ROUTE
  • HAKMEM_DEBUG
  • HAKMEM_DEBUG_LEVEL
  • HAKMEM_DEBUG_TINY
  • HAKMEM_EXPERIMENTAL_ADAPTIVE_DRAIN
  • HAKMEM_EXPERIMENTAL_CACHE_TUNING
  • HAKMEM_FORCE_LIBC
  • HAKMEM_INTEGRITY_CHECKS
  • HAKMEM_LEARN_ADVANCED
  • HAKMEM_LEARN_DECAY
  • HAKMEM_MEM_LEARN
  • HAKMEM_MEM_LEARN_THRESHOLD
  • HAKMEM_MEM_LEARN_WINDOW
  • HAKMEM_PROFILE_SYSCALLS
  • HAKMEM_STATS_ENABLE (docs/archive のみ・現行コードでは未使用、備考コメントに変更済み)
  • HAKMEM_STATS_INTERVAL_SEC (同上)
  • HAKMEM_STATS_VERBOSE

How We Verified

  1. rg 'getenv\\(\"HAKMEM_' core include src tools -n --sort path → 0 matches for all 21 names.
  2. comm -23 docs_env code_env diff to isolate documentation-only names.
  3. Spot-checked docs/specs/ENV_VARS*.md and related papers to ensure these are proposal artifacts, not active flags.

Recommended Cleanup

  • Remove these names from docs/specs/ENV_VARS.md, docs/specs/ENV_VARS_COMPLETE.md, and any status reports when you next touch them (no code changes needed).
  • Keep a single sentence in change logs noting that these toggles never existed in runtime code (A/B rollback not needed).

Notes

  • These were planning placeholders (adaptive tuning knobs, generic debug toggles, and early build-time experiments) that never materialized.
  • Keeping them in docs increases cognitive load; deleting them is a zero-risk, reversible documentation-only change.