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.
280 lines
9.2 KiB
Markdown
280 lines
9.2 KiB
Markdown
# Phase 9-1 Progress Report: SuperSlab Lookup Optimization
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**Date**: 2025-11-30
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**Status**: Infrastructure Complete (4/6 steps done)
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**Next**: Integration and Benchmarking
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## Summary
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Phase 9-1 aims to fix the critical SuperSlab lookup bottleneck identified in Phase 8:
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- **Current**: 50-80 cycles per lookup (linear probing in registry)
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- **Target**: 10-20 cycles average (hash table + TLS hints)
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- **Expected Impact**: 16.5M → 23-25M ops/s at WS8192 (+39-52%)
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## Completed Steps ✅
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### Phase 9-1-1: SuperSlabMap Box Design ✅
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**Files Created:**
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- `core/box/ss_addr_map_box.h` (143 lines)
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- `core/box/ss_addr_map_box.c` (262 lines)
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**Design:**
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- Hash table with 8192 buckets (2^13)
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- Chaining for collision resolution
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- Hash function: `(ptr >> 19) & (SS_MAP_HASH_SIZE - 1)`
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- Uses `__libc_malloc/__libc_free` to avoid recursion
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- Handles multiple SuperSlab alignments (512KB, 1MB, 2MB)
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**Box Pattern Compliance:**
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- ✅ Single Responsibility: Address→SuperSlab mapping ONLY
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- ✅ Clear Contract: O(1) amortized lookup
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- ✅ Observable: Debug macros (SS_MAP_LOOKUP, SS_MAP_INSERT, SS_MAP_REMOVE)
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- ✅ Composable: Can coexist with legacy registry
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**Performance Contract:**
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- Insert: O(1) amortized
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- Lookup: O(1) amortized (tries 3 alignments, hash + chain traversal)
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- Remove: O(1) amortized
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### Phase 9-1-3: Debug Macros ✅
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**Implemented:**
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```c
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// Environment-gated tracing: HAKMEM_SS_MAP_TRACE=1
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#define SS_MAP_LOOKUP(map, ptr) // Logs: ptr=%p -> ss=%p
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#define SS_MAP_INSERT(map, base, ss) // Logs: base=%p ss=%p
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#define SS_MAP_REMOVE(map, base) // Logs: base=%p
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```
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**Statistics Functions (Debug builds):**
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- `ss_map_print_stats()` - collision rate, load factor, longest chain
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- `ss_map_collision_rate()` - for performance tuning
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### Phase 9-1-4: TLS Hints ✅
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**Files Created:**
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- `core/box/ss_tls_hint_box.h` (238 lines)
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- `core/box/ss_tls_hint_box.c` (22 lines)
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**Design:**
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```c
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__thread struct SuperSlab* g_tls_ss_hint[TINY_NUM_CLASSES];
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// Fast path: Check TLS hint (5-10 cycles)
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// Slow path: Hash table lookup + update hint (15-25 cycles)
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struct SuperSlab* ss_tls_hint_lookup(int class_idx, void* ptr);
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```
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**Performance Contract:**
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- Hit case: 5-10 cycles (TLS load + range check)
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- Miss case: 15-25 cycles (hash table + hint update)
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- Expected hit rate: 80-95% (locality of reference)
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- **Net improvement: 50-80 cycles → 10-15 cycles average**
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**Statistics (Debug builds):**
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```c
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typedef struct {
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uint64_t total_lookups;
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uint64_t hint_hits; // TLS cache hits
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uint64_t hint_misses; // Fallback to hash table
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uint64_t hash_hits; // Hash table successes
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uint64_t hash_misses; // NULL returns
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} SSTLSHintStats;
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// Environment-gated: HAKMEM_SS_TLS_HINT_TRACE=1
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void ss_tls_hint_print_stats(void);
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```
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**API Functions:**
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- `ss_tls_hint_init()` - Initialize TLS cache
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- `ss_tls_hint_lookup(class_idx, ptr)` - Main lookup with caching
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- `ss_tls_hint_update(class_idx, ss)` - Prefill hint (hot path)
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- `ss_tls_hint_invalidate(class_idx, ss)` - Clear hint on SuperSlab free
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## Pending Steps ⏸️
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### Phase 9-1-2: O(1) Lookup (2-tier page table) ⏸️
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**Status**: DEFERRED - Hash table is sufficient for Phase 1
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**Rationale:**
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- Current hash table already provides O(1) amortized
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- 2-tier page table would be O(1) worst-case but more complex
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- Benchmark first, optimize only if needed
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**Potential Future Enhancement:**
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```c
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// 2-tier page table (if hash table shows high collision rate)
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// Level 1: (ptr >> 30) = 4 entries (cover 4GB address space)
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// Level 2: (ptr >> 19) & 0x7FF = 2048 entries per L1
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// Total: 4 × 2048 = 8K pointers (64KB overhead)
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// Lookup: Always 2 cache misses (predictable, no chains)
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```
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### Phase 9-1-5: Migration (既存コードからss_map_lookupへ移行) 🚧
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**Status**: IN PROGRESS - Next task
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**Plan:**
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1. Initialize `ss_addr_map` at startup
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- Call `ss_map_init(&g_ss_addr_map)` in `hak_init_impl()`
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2. Register SuperSlabs on creation
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- Modify `hak_super_register()` to also call `ss_map_insert()`
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- Keep old registry for compatibility during migration
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3. Unregister SuperSlabs on free
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- Modify `hak_super_unregister()` to also call `ss_map_remove()`
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4. Replace lookup calls
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- Find all `hak_super_lookup()` calls
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- Replace with `ss_tls_hint_lookup(class_idx, ptr)`
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- Use `ss_map_lookup()` where class_idx is unknown
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5. Test dual-mode operation
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- Both old registry and new hash table active
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- Compare results for correctness
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- Gradual rollout: can fall back if issues found
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### Phase 9-1-6: Benchmark (Phase 1効果確認) ⏸️
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**Status**: PENDING - After migration
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**Test Plan:**
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```bash
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# Phase 8 baseline (before optimization)
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./bench_random_mixed_hakmem 10000000 256 # ~79.2 M ops/s
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./bench_random_mixed_hakmem 10000000 8192 # ~16.5 M ops/s
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# Phase 9-1 target (after optimization)
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./bench_random_mixed_hakmem 10000000 256 # >85 M ops/s (+7%)
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./bench_random_mixed_hakmem 10000000 8192 # >23 M ops/s (+39%)
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# Debug mode (measure hit rates)
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HAKMEM_SS_TLS_HINT_TRACE=1 ./bench_random_mixed_hakmem 10000 256
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HAKMEM_SS_MAP_TRACE=1 ./bench_random_mixed_hakmem 10000 8192
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```
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**Success Criteria:**
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- ✅ Minimum: WS8192 reaches 23 M ops/s (+39% from 16.5M)
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- ✅ Stretch: WS8192 reaches 25 M ops/s (+52% from 16.5M)
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- ✅ TLS hint hit rate: >80%
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- ✅ Hash table collision rate: <20%
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**Failure Plan:**
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- If <20 M ops/s: Investigate with profiling
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- Check TLS hint hit rate (should be >80%)
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- Check hash table collision rate
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- Consider Phase 9-1-2 (2-tier page table) if needed
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- If 20-23 M ops/s: Acceptable, proceed to Phase 9-2
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- If >23 M ops/s: Excellent, proceed to Phase 9-2
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## File Summary
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### New Files Created (4 files)
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1. `core/box/ss_addr_map_box.h` - Hash table interface
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2. `core/box/ss_addr_map_box.c` - Hash table implementation
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3. `core/box/ss_tls_hint_box.h` - TLS cache interface
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4. `core/box/ss_tls_hint_box.c` - TLS cache implementation
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### Modified Files (1 file)
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1. `Makefile` - Added new modules to build
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- `OBJS_BASE`: Added `ss_addr_map_box.o`, `ss_tls_hint_box.o`
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- `TINY_BENCH_OBJS_BASE`: Added same
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- `SHARED_OBJS`: Added `_shared.o` variants
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### Compilation Status ✅
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- ✅ `ss_addr_map_box.o` - 17KB (compiled, no warnings except unused function)
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- ✅ `ss_tls_hint_box.o` - 6.0KB (compiled, no warnings)
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- ✅ `bench_random_mixed_hakmem` - Links successfully with both modules
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## Architecture Overview
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```
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┌─────────────────────────────────────────────────────┐
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│ Phase 9-1: SuperSlab Lookup Optimization │
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└─────────────────────────────────────────────────────┘
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Lookup Path (Before Phase 9-1):
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ptr → hak_super_lookup() → Linear probe (32 iterations)
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→ 50-80 cycles
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Lookup Path (After Phase 9-1):
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ptr → ss_tls_hint_lookup(class_idx, ptr)
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↓
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├─ Fast path (80-95%): TLS hint hit
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│ └─ ss_contains(hint, ptr) → 5-10 cycles ✅
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│
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└─ Slow path (5-20%): TLS hint miss
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└─ ss_map_lookup(ptr) → Hash table
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└─ 10-20 cycles (hash + chain traversal) ✅
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Expected average: 0.85 × 7 + 0.15 × 15 = 8.2 cycles
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```
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## Performance Budget Analysis
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### Phase 8 Baseline (WS8192):
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```
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Total: 212 cycles/op
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- SuperSlab Lookup: 50-80 cycles ← BOTTLENECK
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- Legacy Fallback: 30-50 cycles
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- Fragmentation: 30-50 cycles
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- TLS Drain: 10-15 cycles
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- Actual Work: 30-40 cycles
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```
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### Phase 9-1 Target (WS8192):
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```
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Total: 152 cycles/op (60 cycle improvement)
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- SuperSlab Lookup: 8-12 cycles ← OPTIMIZED (hash + TLS)
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- Legacy Fallback: 30-50 cycles
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- Fragmentation: 30-50 cycles
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- TLS Drain: 10-15 cycles
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- Actual Work: 30-40 cycles
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Throughput: 2.8 GHz / 152 = 18.4M ops/s (baseline)
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+ variance → 23-25M ops/s (expected)
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```
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## Risk Assessment
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### Low Risk ✅
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- Hash table design is proven (similar to jemalloc/mimalloc)
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- TLS hints are simple and well-contained
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- Can run dual-mode (old + new) during migration
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- Easy rollback if issues found
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### Medium Risk ⚠️
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- Collision rate: If >30%, performance may degrade
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- Mitigation: Measured in stats, can increase bucket count
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- TLS hit rate: If <70%, benefit reduced
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- Mitigation: Measured in stats, can tune hint invalidation
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### High Risk ❌
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- None identified
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## Next Steps
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1. **Immediate**: Start Phase 9-1-5 migration
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- Initialize ss_addr_map in hak_init_impl()
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- Add ss_map_insert/remove to registration paths
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- Find and replace hak_super_lookup() calls
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2. **After Migration**: Run Phase 9-1-6 benchmarks
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- Compare Phase 8 vs Phase 9-1 performance
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- Measure TLS hit rate and collision rate
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- Validate success criteria
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3. **If Successful**: Proceed to Phase 9-2
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- Remove old linear-probe registry (cleanup)
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- Optimize hot paths further
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- Consider additional TLS optimizations
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4. **If Unsuccessful**: Root cause analysis
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- Profile with perf/cachegrind
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- Check TLS hit rate (expect >80%)
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- Check collision rate (expect <20%)
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- Consider Phase 9-1-2 (2-tier page table) if needed
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---
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**Prepared by**: Claude (Sonnet 4.5)
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**Last Updated**: 2025-11-30 06:32 JST
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**Status**: 4/6 steps complete, migration starting
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