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.
CRITICAL BUG FIX: Phase E1 introduced 1-byte headers for ALL size classes (C0-C7),
changing the pointer contract. However, many locations still called slab_index_for()
with USER pointers (storage+1) instead of BASE pointers (storage), causing off-by-one
slab index calculations that corrupted memory.
Root Cause:
- USER pointer = BASE + 1 (returned by malloc, points past header)
- BASE pointer = storage start (where 1-byte header is written)
- slab_index_for() expects BASE pointer for correct slab boundary calculations
- Passing USER pointer → wrong slab_idx → wrong metadata → freelist corruption
Impact Before Fix:
- bench_random_mixed crashes at ~14K iterations with SEGV
- Massive C7 alignment check failures (wrong slab classification)
- Memory corruption from writing to wrong slab freelists
Fixes Applied (8 locations):
1. core/hakmem_tiny_free.inc:137
- Added USER→BASE conversion before slab_index_for()
2. core/hakmem_tiny_ultra_simple.inc:148
- Added USER→BASE conversion before slab_index_for()
3. core/tiny_free_fast.inc.h:220
- Added USER→BASE conversion before slab_index_for()
4-5. core/tiny_free_magazine.inc.h:126,315
- Added USER→BASE conversion before slab_index_for() (2 locations)
6. core/box/free_local_box.c:14,22,62
- Added USER→BASE conversion before slab_index_for()
- Fixed delta calculation to use BASE instead of USER
- Fixed debug logging to use BASE instead of USER
7. core/hakmem_tiny.c:448,460,473 (tiny_debug_track_alloc_ret)
- Added USER→BASE conversion before slab_index_for() (2 calls)
- Fixed delta calculation to use BASE instead of USER
- This function is called on EVERY allocation in debug builds
Results After Fix:
✅ bench_random_mixed stable up to 66K iterations (~4.7x improvement)
✅ C7 alignment check failures eliminated (was: 100% failure rate)
✅ Front Gate "Unknown" classification dropped to 0% (was: 1.67%)
✅ No segfaults for workloads up to ~33K allocations
Remaining Issue:
❌ Segfault still occurs at iteration 66152 (allocs=33137, frees=33014)
- Different bug from USER/BASE conversion issues
- Likely capacity/boundary condition (further investigation needed)
Testing:
- bench_random_mixed_hakmem 1K-66K iterations: PASS
- bench_random_mixed_hakmem 67K+ iterations: FAIL (different bug)
- bench_fixed_size_hakmem 200K iterations: PASS
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
- core/hakmem_tiny_fastcache.inc.h: make tiny_fast_pop/push read/write next at base+1 for C0–C6; clear C7 next on pop
- core/hakmem_tiny_hot_pop.inc.h: header-aware next reads for g_fast_head pops (classes 0–3)
- core/tiny_free_magazine.inc.h: header-aware chain linking for BG spill chain (base+1 for C0–C6)
- core/box/front_gate_classifier.c: registry fallback classifies headerless only for class 7; others as headered
Build OK; bench_fixed_size_hakmem still SIGBUS right after init. FREE_ROUTE trace shows invalid frees (ptr=0xa0, etc.). Next steps: instrument early frees and audit remaining header-aware writes in any front caches not yet patched.
