- Redefine TinyHotHeap v2 as per-thread Hot Box with clear boundaries
- Add comprehensive OS statistics tracking for SS allocations
- Implement route-based free handling for TinyHeap v2
- Add C6/C7 debugging and statistics improvements
- Update documentation with implementation guidelines and analysis
- Add new box headers for stats, routing, and front-end management
## Implementation
- Added MADV_DONTNEED when SuperSlab enters LRU cache
- Environment variable: HAKMEM_SS_LAZY_ZERO (default: 1)
- Low-risk, zero-overhead when disabled
## Results: NO MEASURABLE IMPROVEMENT
- Cycles: 70.4M (baseline) vs 70.8M (optimized) = -0.5% (worse!)
- Page faults: 7,674 (no change)
- L1 misses: 717K vs 714K (negligible)
## Key Discovery
The 11.65% clear_page_erms overhead is **kernel-level**, not allocator-level:
- Happens during page faults, not during free
- Can't be selectively deferred for SuperSlab pages
- MADV_DONTNEED syscall overhead cancels benefit
- Result: Zero improvement despite profiling showing 11.65%
## Why Profiling Was Misleading
- Page zeroing shown in profile but not controllable
- Happens globally across all allocators
- Can't isolate which faults are from our code
- Not all profile % are equally optimizable
## Conclusion
Random Mixed 1.06M ops/s appears to be near the practical limit:
- THP: no effect (already tested)
- PREFAULT: +2.6% (measurement noise)
- Lazy zeroing: 0% (syscall overhead cancels benefit)
- Realistic cap: ~1.10-1.15M ops/s (10-15% max possible)
Tiny Hot (89M ops/s) is not comparable - it's an architectural difference.
🐱 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
Major breakthrough: sh8bench now completes without SIGSEGV!
Added defensive refcounting and failsafe mechanisms to prevent
use-after-free and corruption propagation.
Changes:
1. SuperSlab Refcount Pinning (core/box/tls_sll_box.h)
- tls_sll_push_impl: increment refcount before adding to list
- tls_sll_pop_impl: decrement refcount when removing from list
- Prevents SuperSlab from being freed while TLS SLL holds pointers
2. SuperSlab Release Guards (core/superslab_allocate.c, shared_pool_release.c)
- Check refcount > 0 before freeing SuperSlab
- If refcount > 0, defer release instead of freeing
- Prevents use-after-free when TLS/remote/freelist hold stale pointers
3. TLS SLL Next Pointer Validation (core/box/tls_sll_box.h)
- Detect invalid next pointer during traversal
- Log [TLS_SLL_NEXT_INVALID] when detected
- Drop list to prevent corruption propagation
4. Unified Cache Freelist Validation (core/front/tiny_unified_cache.c)
- Validate freelist head before use
- Log [UNIFIED_FREELIST_INVALID] for corrupted lists
- Defensive drop to prevent bad allocations
5. Early Refcount Decrement Fix (core/tiny_free_fast.inc.h)
- Removed ss_active_dec_one from fast path
- Prevents premature refcount depletion
- Defers decrement to proper cleanup path
Test Results:
✅ sh8bench completes successfully (exit code 0)
✅ No SIGSEGV or ABORT signals
✅ Short runs (5s) crash-free
⚠️ Multiple [TLS_SLL_NEXT_INVALID] / [UNIFIED_FREELIST_INVALID] logged
⚠️ Invalid pointers still present (stale references exist)
Status Analysis:
- Stability: ACHIEVED (no crashes)
- Root Cause: NOT FULLY SOLVED (invalid pointers remain)
- Approach: Defensive + refcount guards working well
Remaining Issues:
❌ Why does SuperSlab get unregistered while TLS SLL holds pointers?
❌ SuperSlab lifecycle: remote_queue / adopt / LRU interactions?
❌ Stale pointers indicate improper SuperSlab lifetime management
Performance Impact:
- Refcount operations: +1-3 cycles per push/pop (minor)
- Validation checks: +2-5 cycles (minor)
- Overall: < 5% overhead estimated
Next Investigation:
- Trace SuperSlab lifecycle (allocation → registration → unregister → free)
- Check remote_queue handling
- Verify adopt/LRU mechanisms
- Correlate stale pointer logs with SuperSlab unregister events
Log Volume Warning:
- May produce many diagnostic logs on long runs
- Consider ENV gating for production
Technical Notes:
- Refcount is per-SuperSlab, not global
- Guards prevent symptom propagation, not root cause
- Root cause is in SuperSlab lifecycle management
🤖 Generated with Claude Code (https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
ChatGPT's diagnostic changes to address TLS_SLL_HDR_RESET issue.
Current status: Partial mitigation, but root cause remains.
Changes Applied:
1. SuperSlab Registry Fallback (hakmem_super_registry.h)
- Added legacy table probe when hash map lookup misses
- Prevents NULL returns for valid SuperSlabs during initialization
- Status: ✅ Works but may hide underlying registration issues
2. TLS SLL Push Validation (tls_sll_box.h)
- Reject push if SuperSlab lookup returns NULL
- Reject push if class_idx mismatch detected
- Added [TLS_SLL_PUSH_NO_SS] diagnostic message
- Status: ✅ Prevents list corruption (defensive)
3. SuperSlab Allocation Class Fix (superslab_allocate.c)
- Pass actual class_idx to sp_internal_allocate_superslab
- Prevents dummy class=8 causing OOB access
- Status: ✅ Root cause fix for allocation path
4. Debug Output Additions
- First 256 push/pop operations traced
- First 4 mismatches logged with details
- SuperSlab registration state logged
- Status: ✅ Diagnostic tool (not a fix)
5. TLS Hint Box Removed
- Deleted ss_tls_hint_box.{c,h} (Phase 1 optimization)
- Simplified to focus on stability first
- Status: ⏳ Can be re-added after root cause fixed
Current Problem (REMAINS UNSOLVED):
- [TLS_SLL_HDR_RESET] still occurs after ~60 seconds of sh8bench
- Pointer is 16 bytes offset from expected (class 1 → class 2 boundary)
- hak_super_lookup returns NULL for that pointer
- Suggests: Use-After-Free, Double-Free, or pointer arithmetic error
Root Cause Analysis:
- Pattern: Pointer offset by +16 (one class 1 stride)
- Timing: Cumulative problem (appears after 60s, not immediately)
- Location: Header corruption detected during TLS SLL pop
Remaining Issues:
⚠️ Registry fallback is defensive (may hide registration bugs)
⚠️ Push validation prevents symptoms but not root cause
⚠️ 16-byte pointer offset source unidentified
Next Steps for Investigation:
1. Full pointer arithmetic audit (Magazine ⇔ TLS SLL paths)
2. Enhanced logging at HDR_RESET point:
- Expected vs actual pointer value
- Pointer provenance (where it came from)
- Allocation trace for that block
3. Verify Headerless flag is OFF throughout build
4. Check for double-offset application in conversions
Technical Assessment:
- 60% root cause fixes (allocation class, validation)
- 40% defensive mitigation (registry fallback, push rejection)
Performance Impact:
- Registry fallback: +10-30 cycles on cold path (negligible)
- Push validation: +5-10 cycles per push (acceptable)
- Overall: < 2% performance impact estimated
Related Issues:
- Phase 1 TLS Hint Box removed temporarily
- Phase 2 Headerless blocked until stability achieved
🤖 Generated with Claude Code (https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
Add active field to TinySlabMeta to track blocks currently held by
users (not in TLS SLL or freelist caches). This enables accurate
empty slab detection that accounts for TLS SLL cached blocks.
Changes:
- superslab_types.h: Add _Atomic uint16_t active field
- ss_allocation_box.c, hakmem_tiny_superslab.c: Initialize active=0
- tiny_free_fast_v2.inc.h: Decrement active on TLS SLL push
- tiny_alloc_fast.inc.h: Add tiny_active_track_alloc() helper,
increment active on TLS SLL pop (all code paths)
- ss_hot_cold_box.h: ss_is_slab_empty() uses active when enabled
All tracking is ENV-gated: HAKMEM_TINY_ACTIVE_TRACK=1 to enable.
Default is off for zero performance impact.
Invariant: active = used - tls_cached (active <= used)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
