Phase FREE-LEGACY-OPT-6: C4 ULTRA Implementation
Implement C4 ULTRA free TLS cache with parasitic free+alloc pattern,
achieving 99.7-99.9% elimination of C4 legacy fallback calls.
Key Features:
- TLS cache cap=64 (tuned for L1 cache fit, smaller than C5/C6's 128)
- Segment learning via ss_fast_lookup() on first free
- Free-side cache push + alloc-side TLS pop pattern
- ENV gate: HAKMEM_TINY_C4_ULTRA_FREE_ENABLED (default OFF)
- Full FREE_PATH_STATS instrumentation
Benchmark Results:
C4-heavy (65-128B range):
- C4 legacy: 591,583 → 1,711 (-99.7%)
- c4_ultra cache hits: ~599k (free) + ~599k (alloc)
- Mixed load: 340,732 → 284 C4 legacy (-99.9%)
Legacy fallback reduction:
- C4-heavy: 589,872 fewer legacy calls (-10.9% total)
- Mixed: 340,448 fewer C4 legacy calls (-12.8% in mixed)
Performance note: ~2% throughput cost in isolated C4-heavy case,
acceptable tradeoff for 99%+ legacy elimination per class.
Files:
NEW: core/box/tiny_c4_ultra_free_box.h/c
NEW: core/box/tiny_c4_ultra_free_env_box.h
MOD: core/box/tiny_ultra_classes_box.h (added C4 macros)
MOD: core/box/free_path_stats_box.h/c (C4 ULTRA counters)
MOD: core/front/malloc_tiny_fast.h (C4 alloc+free integration)
MOD: Makefile (added C4 ULTRA object)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
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