8786d58fc8
Summary: ======== Phase 17-2 implements dedicated SuperSlab backend for Small-Mid allocator (256B-1KB). Result: No performance improvement (-0.9%), worse than Phase 17-1 (+0.3%). Root cause: 70% page fault (ChatGPT + perf profiling). Conclusion: Small-Mid専用層戦略は失敗。Tiny SuperSlab最適化が必要。 Implementation: =============== 1. Dedicated Small-Mid SuperSlab pool (1MB, 16 slabs/SS) - Separate from Tiny SuperSlab (no competition) - Batch refill (8-16 blocks per TLS refill) - Direct 0xb0 header writes (no Tiny delegation) 2. Backend architecture - SmallMidSuperSlab: 1MB aligned region, fast ptr→SS lookup - SmallMidSlabMeta: per-slab metadata (capacity/used/carved/freelist) - SmallMidSSHead: per-class pool with LRU tracking 3. Batch refill implementation - smallmid_refill_batch(): 8-16 blocks/call (vs 1 in Phase 17-1) - Freelist priority → bump allocation fallback - Auto SuperSlab expansion when exhausted Files Added: ============ - core/hakmem_smallmid_superslab.h: SuperSlab metadata structures - core/hakmem_smallmid_superslab.c: Backend implementation (~450 lines) Files Modified: =============== - core/hakmem_smallmid.c: Removed Tiny delegation, added batch refill - Makefile: Added hakmem_smallmid_superslab.o to build - CURRENT_TASK.md: Phase 17 完了記録 + Phase 18 計画 A/B Benchmark Results: ====================== | Size | Phase 17-1 (ON) | Phase 17-2 (ON) | Delta | vs Baseline | |--------|-----------------|-----------------|----------|-------------| | 256B | 6.06M ops/s | 5.84M ops/s | -3.6% | -4.1% | | 512B | 5.91M ops/s | 5.86M ops/s | -0.8% | +1.2% | | 1024B | 5.54M ops/s | 5.44M ops/s | -1.8% | +0.4% | | Avg | 5.84M ops/s | 5.71M ops/s | -2.2% | -0.9% | Performance Analysis (ChatGPT + perf): ====================================== ✅ Frontend (TLS/batch refill): OK - Only 30% CPU time - Batch refill logic is efficient - Direct 0xb0 header writes work correctly ❌ Backend (SuperSlab allocation): BOTTLENECK - 70% CPU time in asm_exc_page_fault - mmap(1MB) → kernel page allocation → very slow - New SuperSlab allocation per benchmark run - No warm SuperSlab reuse (used counter never decrements) Root Cause: =========== Small-Mid allocates new SuperSlabs frequently: alloc → TLS miss → refill → new SuperSlab → mmap(1MB) → page fault (70%) Tiny reuses warm SuperSlabs: alloc → TLS miss → refill → existing warm SuperSlab → no page fault Key Finding: "70% page fault" reveals SuperSlab layer needs optimization, NOT frontend layer (TLS/batch refill design is correct). Lessons Learned: ================ 1. ❌ Small-Mid専用層戦略は失敗 (Phase 17-1: +0.3%, Phase 17-2: -0.9%) 2. ✅ Frontend実装は成功 (30% CPU, batch refill works) 3. 🔥 70% page fault = SuperSlab allocation bottleneck 4. ✅ Tiny (6.08M ops/s) is already well-optimized, hard to beat 5. ✅ Layer separation doesn't improve performance - backend optimization needed Next Steps (Phase 18): ====================== ChatGPT recommendation: Optimize Tiny SuperSlab (NOT Small-Mid specific layer) Box SS-Reuse (Priority 1): - Implement meta->freelist reuse (currently bump-only) - Detect slab empty → return to shared_pool - Reuse same SuperSlab for longer (reduce page faults) - Target: 70% page fault → 5-10%, 2-4x improvement Box SS-Prewarm (Priority 2): - Pre-allocate SuperSlabs per class (Phase 11: +6.4%) - Concentrate page faults at benchmark start - Benchmark-only optimization Small-Mid Implementation Status: ================================= - ENV=0 by default (zero overhead, branch predictor learns) - Complete separation from Tiny (no interference) - Valuable as experimental record ("why dedicated layer failed") - Can be removed later if needed (not blocking Tiny optimization) 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
14 lines
484 B
Makefile
14 lines
484 B
Makefile
hakmem_smallmid.o: core/hakmem_smallmid.c core/hakmem_smallmid.h \
|
|
core/hakmem_build_flags.h core/hakmem_smallmid_superslab.h \
|
|
core/tiny_region_id.h core/tiny_box_geometry.h \
|
|
core/hakmem_tiny_superslab_constants.h core/hakmem_tiny_config.h \
|
|
core/ptr_track.h
|
|
core/hakmem_smallmid.h:
|
|
core/hakmem_build_flags.h:
|
|
core/hakmem_smallmid_superslab.h:
|
|
core/tiny_region_id.h:
|
|
core/tiny_box_geometry.h:
|
|
core/hakmem_tiny_superslab_constants.h:
|
|
core/hakmem_tiny_config.h:
|
|
core/ptr_track.h:
|