d2f0d84584
## Problem: 53-byte misalignment mystery **Symptom:** All SuperSlab allocations misaligned by exactly 53 bytes ``` [TRC_FAILFAST_PTR] stage=alloc_ret_align cls=7 ptr=0x..f835 offset=63541 (expected: 63488) Diff: 63541 - 63488 = 53 bytes ``` ## Root Cause (Ultrathink investigation) **sizeof(SuperSlab) != hardcoded offset:** - `sizeof(SuperSlab)` = 1088 bytes (actual struct size) - `tiny_slab_base_for()` used: 1024 (hardcoded) - `superslab_init_slab()` assumed: 2048 (in capacity calc) **Impact:** 1. Memory corruption: 64-byte overlap with SuperSlab metadata 2. Misalignment: 1088 % 1024 = 64 (violates class 7 alignment) 3. Inconsistency: Init assumed 2048, but runtime used 1024 ## Solution ### 1. Centralize constants (NEW) **File:** `core/hakmem_tiny_superslab_constants.h` - `SLAB_SIZE` = 64KB - `SUPERSLAB_HEADER_SIZE` = 1088 - `SUPERSLAB_SLAB0_DATA_OFFSET` = 2048 (aligned to 1024) - `SUPERSLAB_SLAB0_USABLE_SIZE` = 63488 (64KB - 2048) - Compile-time validation checks **Why 2048?** - Round up 1088 to next 1024-byte boundary - Ensures proper alignment for class 7 (1024-byte blocks) - Previous: (1088 + 1023) & ~1023 = 2048 ### 2. Update all code to use constants - `hakmem_tiny_superslab.h`: `tiny_slab_base_for()` → use `SUPERSLAB_SLAB0_DATA_OFFSET` - `hakmem_tiny_superslab.c`: `superslab_init_slab()` → use `SUPERSLAB_SLAB0_USABLE_SIZE` - Removed hardcoded 1024, 2048 magic numbers ### 3. Add class consistency check **File:** `core/tiny_superslab_alloc.inc.h:433-449` - Verify `tls->ss->size_class == class_idx` before allocation - Unbind TLS if mismatch detected - Prevents using wrong block_size for calculations ## Status ⚠️ **INCOMPLETE - New issue discovered** After fix, benchmark hits different error: ``` [TRC_FAILFAST] stage=freelist_next cls=7 node=0x...d474 ``` Freelist corruption detected. Likely caused by: - 2048 offset change affects free() path - Block addresses no longer match freelist expectations - Needs further investigation ## Files Modified - `core/hakmem_tiny_superslab_constants.h` - NEW: Centralized constants - `core/hakmem_tiny_superslab.h` - Use SUPERSLAB_SLAB0_DATA_OFFSET - `core/hakmem_tiny_superslab.c` - Use SUPERSLAB_SLAB0_USABLE_SIZE - `core/tiny_superslab_alloc.inc.h` - Add class consistency check - `core/hakmem_tiny_init.inc` - Remove diet mode override (Phase 6-2.5) - `core/hakmem_super_registry.h` - Remove debug output (cleaned) - `PERFORMANCE_INVESTIGATION_REPORT.md` - Task agent analysis ## Next Steps 1. Investigate freelist corruption with 2048 offset 2. Verify free() path uses tiny_slab_base_for() correctly 3. Consider reverting to 1024 and fixing capacity calculation instead 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
60 lines
2.3 KiB
C
60 lines
2.3 KiB
C
// hakmem_tiny_superslab_constants.h - SuperSlab Layout Constants
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// Purpose: Centralize all SuperSlab layout magic numbers
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// Phase 6-2.5: Created to fix sizeof(SuperSlab) vs hardcoded offset mismatch
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#ifndef HAKMEM_TINY_SUPERSLAB_CONSTANTS_H
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#define HAKMEM_TINY_SUPERSLAB_CONSTANTS_H
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// ============================================================================
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// SuperSlab Layout Constants
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// ============================================================================
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// Size of each slab within SuperSlab (fixed, never changes)
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#define SLAB_SIZE (64 * 1024) // 64KB per slab
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// SuperSlab struct size (as of Phase 6-2.5)
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// Actual value: sizeof(SuperSlab) = 1088 bytes
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// This includes: magic, lg_size, size_class, total_active_blocks,
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// remote_heads[], slabs[], slab_listed[], etc.
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#define SUPERSLAB_HEADER_SIZE 1088
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// Slab 0 data offset (CRITICAL: Must be aligned to largest block size)
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// Phase 6-2.5 FIX: Changed from 1024 to 2048
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//
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// Why 2048?
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// - sizeof(SuperSlab) = 1088 bytes
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// - Largest block size = 1024 bytes (class 7)
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// - Must round up to next 1024-byte boundary: (1088 + 1023) & ~1023 = 2048
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//
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// Layout:
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// [0..1087] SuperSlab header (1088 bytes)
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// [1088..2047] Padding (960 bytes, unused)
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// [2048..65535] Slab 0 data (63488 bytes = 64KB - 2048)
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//
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// Previous value (1024) caused:
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// - 64-byte overlap with SuperSlab metadata (corruption)
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// - Misalignment for class 7 allocations (1024 % 1024 != 0)
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#define SUPERSLAB_SLAB0_DATA_OFFSET 2048
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// Slab 0 usable size (for capacity calculation)
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#define SUPERSLAB_SLAB0_USABLE_SIZE (SLAB_SIZE - SUPERSLAB_SLAB0_DATA_OFFSET) // 63488 bytes
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// Regular slab (i > 0) usable size
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#define SUPERSLAB_SLAB_USABLE_SIZE SLAB_SIZE // 65536 bytes
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// ============================================================================
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// Validation (compile-time check)
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// ============================================================================
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// Ensure SLAB0_DATA_OFFSET is aligned to largest block size (1024)
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#if (SUPERSLAB_SLAB0_DATA_OFFSET % 1024) != 0
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#error "SUPERSLAB_SLAB0_DATA_OFFSET must be 1024-byte aligned for class 7"
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#endif
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// Ensure SLAB0_DATA_OFFSET is large enough to contain SuperSlab header
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#if SUPERSLAB_SLAB0_DATA_OFFSET < SUPERSLAB_HEADER_SIZE
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#error "SUPERSLAB_SLAB0_DATA_OFFSET must be >= sizeof(SuperSlab)"
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#endif
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#endif // HAKMEM_TINY_SUPERSLAB_CONSTANTS_H
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