TLSF Memory Allocator

Two-Level Segregated Fit Memory Allocator - A deterministic, real-time memory allocator with O(1) allocation/deallocation performance and low fragmentation.

Table of Contents

• Overview
• ✨ Features
• 🚀 Quick Start
• 🔧 Build Instructions
• 📖 API Usage
• 🎯 Algorithm Flow
• 🏗️ Architecture
• 📊 Performance
• 🧪 Testing
• 📁 Project Structure
• 🤝 Contributing
• 📄 License

Overview

TLSF (Two-Level Segregated Fit) is a real-time memory allocator designed for deterministic performance and low fragmentation. Originally developed for embedded and real-time systems, this implementation provides predictable O(1) allocation and deallocation times with bounded worst-case execution.

// Simple Example
void* memory = malloc(1024 * 1024);  // 1MB pool
tlsf_t pool = tlsf_create(memory, 1024 * 1024);
void* ptr = tlsf_malloc(pool, 256);
// Use memory...
tlsf_free(pool, ptr);
tlsf_destroy(pool);

Features

Core Features

• ⚡ O(1) Operations - Constant time allocation and deallocation
• 📉 Low Fragmentation - Efficient memory utilization with two-level segregation
• ⏱️ Deterministic Performance - Predictable worst-case execution time
• 🔒 Thread Safety - Optional mutex protection for concurrent access
• 🏗️ Small Overhead - Minimal metadata (~16 bytes per block)
• 🌐 Platform Independent - Portable across different architectures

Advanced Features

• 🔧 Configurable Parameters - Tune for specific use cases
• 🐛 Debug Support - Memory filling patterns and integrity checks
• 📊 Statistics - Runtime performance metrics (optional)
• 🎯 Aligned Allocation - Support for arbitrary alignment requirements
• 🔄 Reallocation - In-place expansion when possible

Quick Start

Prerequisites

• CMake 3.10+
• C compiler (GCC, Clang, or MSVC)
• Standard C library

Basic Installation

# Clone the repository
git clone https://github.com/yourusername/tlsf-allocator.git
cd tlsf-allocator

# Build
mkdir build && cd build
cmake ..
make

# Run tests
ctest --output-on-failure

Integration into Your Project

# In your CMakeLists.txt
add_subdirectory(tlsf-allocator)
target_link_libraries(your_project tlsf)

Build Instructions

Build Options

# Basic build
cmake -B build .

# With tests and examples
cmake -B build -DTLSF_BUILD_TESTS=ON -DTLSF_BUILD_EXAMPLES=ON .

# As shared library
cmake -B build -DTLSF_BUILD_SHARED=ON .

# Custom configuration
cmake -B build \
  -DTLSF_ALIGN_SIZE=16 \
  -DTLSF_MIN_BLOCK_SIZE=64 \
  -DTLSF_USE_LOCKS=OFF

Platform Support

• Linux/Unix: Full support with pthreads
• Windows: Support via Win32 API
• Embedded: Bare-metal configurations available
• macOS: Full compatibility

API Usage

Basic Operations

#include "tlsf.h"

// Create a memory pool (1MB)
void* memory = malloc(1024 * 1024);
tlsf_t pool = tlsf_create(memory, 1024 * 1024);

// Allocate memory
void* data = tlsf_malloc(pool, 1024);
if (data) {
    memset(data, 0, 1024);
    
    // Reallocate
    data = tlsf_realloc(pool, data, 2048);
    
    // Free
    tlsf_free(pool, data);
}

// Cleanup
tlsf_destroy(pool);
free(memory);

Advanced Usage

// Aligned allocation for SIMD/GPU
void* aligned = tlsf_memalign(pool, 64, 4096);

// Get block information
size_t actual_size = tlsf_block_size(pool, ptr);

// Check pool health
if (!tlsf_check(pool)) {
    printf("Memory corruption detected!\n");
}

// Measure fragmentation
float frag = tlsf_fragmentation(pool);
printf("Fragmentation: %.1f%%\n", frag);

// Iterate through all blocks
tlsf_walk_pool(pool, my_callback, user_data);

Algorithm Flow

Allocation Process

graph TD
    A[Allocation Request] --> B[Adjust for Alignment]
    B --> C[Map Size to FL/SL<br/>Two-Level Segregation]
    C --> D[Search Bitmaps<br/>Find Suitable Free List]
    D --> E{Block Found?}
    E -->|Yes| F[Remove from Free List]
    E -->|No| G[Return NULL]
    F --> H[Split if Too Large]
    H --> I[Mark as Used]
    I --> J[Return Pointer]

Loading

Deallocation Process

graph TD
    A[Free Request] --> B[Get Block Header]
    B --> C[Mark as Free]
    C --> D[Merge with Previous<br/>if Free]
    D --> E[Merge with Next<br/>if Free]
    E --> F[Insert into Free List]
    F --> G[Update Bitmaps]

Loading

📊 Two-Level Segregation

Size Classes:
┌─────────────────────────────────────────┐
│ First Level (FL): Logarithmic classes   │
│   2^6, 2^7, 2^8, ..., 2^19 bytes       │
├─────────────────────────────────────────┤
│ Second Level (SL): Linear sub-classes   │
│   Each FL divided into 256 equal parts  │
└─────────────────────────────────────────┘

Example: 1000 byte request
→ FL = 2^10 (1024) class
→ SL = specific sub-range within 1024

Architecture

Memory Pool Layout

┌─────────────────────────────────────┐
│         Control Structure           │
│  • Bitmaps (FL/SL)                  │
│  • Free list heads                  │
│  • Statistics                       │
│  • Lock (if enabled)                │
├─────────────────────────────────────┤
│         Block Header 1              │
│  • Previous size                    │
│  • Current size + status            │
│  • Free list pointers               │
├─────────────────────────────────────┤
│         User Data 1                 │
├─────────────────────────────────────┤
│         Block Header 2              │
├─────────────────────────────────────┤
│         User Data 2                 │
├─────────────────────────────────────┤
│                ...                  │
└─────────────────────────────────────┘

Configuration Parameters

Parameter	Default	Description
TLSF_ALIGN_SIZE	8	Memory alignment (power of 2)
TLSF_MIN_BLOCK_SIZE	32	Minimum allocatable block
TLSF_FL_INDEX_COUNT	14	First-level size classes
TLSF_SL_INDEX_COUNT	8	Second-level sub-classes
TLSF_USE_LOCKS	1	Enable thread safety
TLSF_DEBUG	0	Enable debug features
TLSF_STATISTICS	0	Collect runtime statistics

Performance

Benchmark Results

Allocation Performance (Intel i7, 3.4GHz):
• Small allocations (16-128 bytes): ~25M ops/sec
• Medium allocations (1-4KB): ~18M ops/sec
• Large allocations (16-64KB): ~12M ops/sec

Memory Overhead:
• Per pool: ~1KB
• Per block: 16 bytes
• Alignment padding: 0-15 bytes

Fragmentation Analysis

Test Scenario: 1MB pool, 1000 random allocations
• Worst-case fragmentation: < 15%
• Average fragmentation: < 5%
• Coalescing efficiency: > 95%

Use Case Performance

Use Case	Performance	Fragmentation
Real-time systems	⭐⭐⭐⭐⭐	⭐⭐⭐⭐⭐
Game engines	⭐⭐⭐⭐⭐	⭐⭐⭐⭐
Embedded devices	⭐⭐⭐⭐⭐	⭐⭐⭐⭐⭐
High-frequency trading	⭐⭐⭐⭐⭐	⭐⭐⭐⭐

Testing

Test Suite

# Run all tests
./build/test_basic
./build/test_stress
./build/test_fragmentation

# With verbose output
ctest -V

# Memory leak detection (Linux)
valgrind --leak-check=full ./build/test_basic

Test Coverage

• Unit Tests: Basic API functionality
• Stress Tests: High-frequency allocation patterns
• Fragmentation Tests: Memory utilization analysis
• Concurrency Tests: Thread-safe operations
• Boundary Tests: Edge cases and error conditions

Debug Features

// Enable debug mode
#define TLSF_DEBUG 1

// Features enabled:
// • Memory filling patterns (0xAA for allocated, 0x55 for free)
// • Boundary checks
// • Double-free detection
// • Pool integrity verification

Project Structure

tlsf-memory-allocator/
├── include/                 # Public headers
│   ├── tlsf.h              # Main API
│   ├── tlsf_config.h       # Configuration
│   └── tlsf_types.h        # Type definitions
├── src/                    # Core implementation
│   ├── tlsf.c             # Pool management
│   ├── tlsf_block.c       # Block operations
│   ├── tlsf_mapping.c     # Size mapping
│   └── tlsf_bitmap.c      # Bitmap operations
├── platform/              # Platform abstraction
│   ├── tlsf_platform.h    # Platform API
│   └── tlsf_platform.c    # Platform implementations
├── tests/                 # Test suite
│   ├── test_basic.c       # Basic functionality
│   ├── test_stress.c      # Stress tests
│   └── test_fragmentation.c # Fragmentation tests
├── examples/              # Usage examples
│   └── simple_usage.c     # Basic example
├── docs/                  # Documentation
│   ├── design.md          # Algorithm design
│   ├── flow.md            # Flow diagrams
│   └── api.md             # API reference
└── CMakeLists.txt         # Build configuration

Use Cases

Game Development

// Game engine memory management
tlsf_t game_pool = tlsf_create(game_memory, 256 * 1024 * 1024);

// Level loading: allocate textures, meshes, sounds
void* texture_data = tlsf_memalign(game_pool, 16, texture_size);
void* mesh_data = tlsf_malloc(game_pool, vertex_count * sizeof(Vertex));

Embedded Systems

// Bare-metal embedded system
#define HEAP_SIZE (128 * 1024)
static uint8_t system_heap[HEAP_SIZE];
tlsf_t system_pool = tlsf_create(system_heap, HEAP_SIZE);

// Real-time task allocation
void* task_stack = tlsf_malloc(system_pool, TASK_STACK_SIZE);
void* task_data = tlsf_malloc(system_pool, sizeof(task_context_t));

Networking

// Network packet pool
tlsf_t packet_pool = tlsf_create(packet_buffer, 64 * 1024);

// Allocate packets with alignment for DMA
void* packet = tlsf_memalign(packet_pool, 64, MAX_PACKET_SIZE);

Advanced Configuration

Custom Pool Size Classes

// In tlsf_config.h
#define TLSF_FL_INDEX_COUNT 12    // Fewer classes for small systems
#define TLSF_SL_INDEX_COUNT 4     // Less granularity
#define TLSF_MIN_BLOCK_SIZE 64    // Larger minimum for specific use case

Thread Safety Options

// Single-threaded (no locking overhead)
#define TLSF_USE_LOCKS 0

// Multi-threaded with custom mutex
// Implement in tlsf_platform.c
void tlsf_mutex_lock(tlsf_mutex_t* mutex) {
    your_custom_lock(mutex);
}

Comparison with Other Allocators

Feature	TLSF	dlmalloc	jemalloc	tcmalloc
O(1) Operations	✅	❌	⚠️	⚠️
Real-time	✅	❌	❌	❌
Fragmentation	Low	Medium	Low	Low
Overhead	Low	Medium	High	Medium
Thread Safety	Optional	Good	Excellent	Excellent
Predictability	Excellent	Poor	Good	Good

Common Pitfalls

Memory Exhaustion

// Always check for allocation failure
void* ptr = tlsf_malloc(pool, size);
if (!ptr) {
    // Handle out-of-memory
    log_error("Failed to allocate %zu bytes", size);
    return ERROR_OUT_OF_MEMORY;
}

Fragmentation Management

// Monitor and manage fragmentation
float frag = tlsf_fragmentation(pool);
if (frag > 30.0f) {
    // Consider: compact memory, increase pool size, or change allocation patterns
    warn_high_fragmentation(frag);
}

Thread Safety

// If TLSF_USE_LOCKS=0, you must ensure thread safety
#ifdef TLSF_USE_LOCKS
    // TLSF handles locking internally
#else
    // You must implement external synchronization
    pthread_mutex_lock(&pool_mutex);
    void* ptr = tlsf_malloc(pool, size);
    pthread_mutex_unlock(&pool_mutex);
#endif

Integration with Standard Libraries

Override malloc/free

// Replace system allocator with TLSF
static tlsf_t global_pool;

void* my_malloc(size_t size) {
    return tlsf_malloc(global_pool, size);
}

void my_free(void* ptr) {
    tlsf_free(global_pool, ptr);
}

Use with C++

// C++ wrapper class
class TLSFAllocator {
private:
    tlsf_t pool;
    
public:
    TLSFAllocator(void* memory, size_t size) {
        pool = tlsf_create(memory, size);
    }
    
    ~TLSFAllocator() {
        tlsf_destroy(pool);
    }
    
    void* allocate(size_t size) {
        return tlsf_malloc(pool, size);
    }
    
    void deallocate(void* ptr) {
        tlsf_free(pool, ptr);
    }
    
    // Optional: aligned allocation
    void* allocate_aligned(size_t size, size_t alignment) {
        return tlsf_memalign(pool, alignment, size);
    }
};

Performance Tuning Tips

1. Pool Sizing: Allocate 10-20% more than your peak usage
2. Alignment: Use appropriate alignment for your data types
3. Allocation Patterns: Allocate similar-sized objects together
4. Free Patterns: Free in reverse allocation order when possible
5. Monitoring: Regularly check fragmentation levels

Debugging Memory Issues

Enable Debug Mode

# Build with debug features
cmake -B build -DTLSF_DEBUG=ON -DCMAKE_BUILD_TYPE=Debug

Common Debug Techniques

// 1. Check pool integrity
assert(tlsf_check(pool));

// 2. Walk and print all blocks
void debug_callback(void* ptr, size_t size, int used, void* data) {
    printf("%s block at %p: %zu bytes\n", 
           used ? "Used" : "Free", ptr, size);
}
tlsf_walk_pool(pool, debug_callback, NULL);

// 3. Use valgrind or address sanitizer
//    Compile with -fsanitize=address

Contributing

We welcome contributions! Here's how you can help:

Reporting Bugs

1. Check existing issues
2. Create a minimal reproduction case
3. Include platform, compiler, and configuration details

Feature Requests

1. Describe the use case
2. Explain the benefit
3. Consider implementation complexity

Code Contributions

1. Fork the repository
2. Create a feature branch
3. Write tests for new functionality
4. Ensure all tests pass
5. Submit a pull request

Code Style

• Follow existing code conventions
• Use meaningful variable names
• Add comments for complex logic
• Include unit tests for new features

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