hakmem/CURRENT_TASK.md

# Current Task: ACE Investigation - Mid-Large Performance Recovery

**Date**: 2025-11-08
**Status**: 🔄 IN PROGRESS
**Priority**: CRITICAL

---

## 🎉 Recent Achievements

### 100% Stability Fix (Commit 616070cf7)
- ✅ **50/50 consecutive 4T runs passed**
- ✅ Bitmap semantics corrected (0xFFFFFFFF = full)
- ✅ Race condition fixed with mutex protection
- ✅ User requirement MET: "5%でもクラッシュおこったら使えない" → **0% crash rate**

### Comprehensive Benchmark Results (2025-11-08)
Located at: `benchmarks/results/comprehensive_20251108_214317/`

**Performance Summary:**

| Category | HAKMEM | vs System | vs mimalloc | Status |
|----------|--------|-----------|-------------|--------|
| **Tiny Hot Path** | 218.65 M/s | **+48.5%** 🏆 | **+23.0%** 🏆 | **HUGE WIN** |
| Random Mixed 128B | 16.92 M/s | 34% | 28% | Good (+3-4x from Phase 6) |
| Random Mixed 256B | 17.59 M/s | 42% | 32% | Good |
| Random Mixed 512B | 15.61 M/s | 42% | 33% | Good |
| Random Mixed 2048B | 11.14 M/s | 50% | 65% | Competitive |
| Random Mixed 4096B | 8.13 M/s | 61% | 66% | Competitive |
| Larson 1T | 3.92 M/s | 28% | - | Needs work |
| Larson 4T | 7.55 M/s | 45% | - | Needs work |
| **Mid-Large MT** | 1.05 M/s | **-88%** 🔴 | **-86%** 🔴 | **CRITICAL ISSUE** |

**Key Findings:**
1. ✅ **First time beating BOTH System and mimalloc** (Tiny Hot Path)
2. ✅ **100% stability** - All benchmarks passed without crashes
3. 🔴 **Critical regression**: Mid-Large MT performance collapsed (-88%)

---

## Objective: Investigate ACE for Mid-Large Performance Recovery

**Problem:**
- Mid-Large MT: 1.05M ops/s (was +171% in docs, now -88%)
- Root cause (from Task Agent report):
  - ACE disabled → all mid allocations go to mmap (slow)
  - This used to be HAKMEM's strength

**Goal:**
- Understand why ACE is disabled
- Determine if re-enabling ACE can recover performance
- If yes, implement ACE enablement
- If no, find alternative optimization

**Note:** HAKX is legacy code, ignore it. Focus on ACE mechanism.

---

## Task for Task Agent (Ultrathink Required)

### Investigation Scope

1. **ACE Current State**
   - Why is ACE disabled?
   - What does ACE do? (Adaptive Cache Engine)
   - How does it help Mid-Large allocations?

2. **Code Analysis**
   - Find ACE enablement flags
   - Find ACE initialization code
   - Find ACE allocation path
   - Understand ACE vs mmap decision

3. **Root Cause**
   - Why does disabling ACE cause -88% regression?
   - What is the overhead of mmap for every allocation?
   - Can we fix this by re-enabling ACE?

4. **Proposed Solution**
   - If ACE can be safely re-enabled: How?
   - If ACE has bugs: What needs fixing?
   - Alternative optimizations if ACE is not viable

5. **Implementation Plan**
   - Step-by-step plan to recover Mid-Large performance
   - Estimated effort (days)
   - Risk assessment

---

## Success Criteria

✅ **Understand ACE mechanism and current state**
✅ **Identify why Mid-Large performance collapsed**
✅ **Propose concrete solution with implementation plan**
✅ **Return detailed analysis report**

---

## Context for Task Agent

**Current Build Flags:**
```bash
make HEADER_CLASSIDX=1 AGGRESSIVE_INLINE=1 PREWARM_TLS=1
```

**Relevant Files to Check:**
- `core/hakmem_ace*.c` - ACE implementation
- `core/hakmem_mid_mt.c` - Mid-Large allocator
- `core/hakmem_learner.c` - Learning mechanism
- Build flags in Makefile

**Benchmark to Verify:**
```bash
# Mid-Large MT (currently broken)
./bench_mid_large_mt_hakmem
# Expected: Should improve significantly with ACE
```

---

## Deliverables

1. **ACE Analysis Report** (markdown)
   - ACE mechanism explanation
   - Current state diagnosis
   - Root cause of -88% regression
   - Proposed solution

2. **Implementation Plan**
   - Concrete steps to fix
   - Code changes needed
   - Testing strategy

3. **Risk Assessment**
   - Stability impact
   - Performance trade-offs
   - Alternative approaches

---

## Timeline

- **Investigation**: Task Agent (Ultrathink mode)
- **Report Review**: 30 min
- **Implementation**: 1-2 days (depends on findings)
- **Validation**: Re-run benchmarks

---

## Notes

- Debug logs now properly guarded with `HAKMEM_SUPERSLAB_VERBOSE`
- Can be enabled with `-DHAKMEM_SUPERSLAB_VERBOSE` for debugging
- Release builds will be clean (no log spam)

---

**Status**: Ready to launch Task Agent investigation 🚀