Memory Layout Optimization

Comprehensive guide to optimizing memory layout for performance in Go applications. This guide covers struct field ordering, memory alignment, cache-friendly data structures, and memory locality optimization.

Table of Contents

Introduction

Memory layout optimization focuses on arranging data structures to maximize CPU cache efficiency, minimize memory footprint, and improve access patterns. Proper memory layout can dramatically improve application performance.

Memory Layout Framework

package main

import (
    "fmt"
    "reflect"
    "runtime"
    "sort"
    "sync"
    "sync/atomic"
    "time"
    "unsafe"
)

// MemoryLayoutAnalyzer provides comprehensive memory layout analysis
type MemoryLayoutAnalyzer struct {
    config       LayoutConfig
    structures   map[string]*StructureInfo
    analyzer     *AlignmentAnalyzer
    optimizer    *LayoutOptimizer
    profiler     *CacheProfiler
    metrics      *LayoutMetrics
    mu           sync.RWMutex
}

// LayoutConfig contains memory layout analysis configuration
type LayoutConfig struct {
    TargetArch       string
    CacheLineSize    int
    PageSize         int
    EnableProfiling  bool
    OptimizeForCache bool
    OptimizeForSize  bool
    AnalyzeDepth     int
}

// StructureInfo contains information about data structure layout
type StructureInfo struct {
    Name          string
    Type          reflect.Type
    Size          uintptr
    Alignment     uintptr
    Fields        []FieldInfo
    Padding       []PaddingInfo
    CacheLines    int
    Fragmentation float64
    Hotness       map[string]int64
    AccessPattern AccessPattern
}

// FieldInfo contains information about struct fields
type FieldInfo struct {
    Name       string
    Type       reflect.Type
    Size       uintptr
    Offset     uintptr
    Alignment  uintptr
    Tag        string
    IsExported bool
    IsPointer  bool
    AccessFreq int64
}

// PaddingInfo contains information about padding bytes
type PaddingInfo struct {
    Offset uintptr
    Size   uintptr
    Reason string
}

// AccessPattern describes how data is accessed
type AccessPattern struct {
    Sequential bool
    Random     bool
    Temporal   bool
    Spatial    bool
    ReadHeavy  bool
    WriteHeavy bool
    HotFields  []string
    ColdFields []string
}

// AlignmentAnalyzer analyzes memory alignment
type AlignmentAnalyzer struct {
    rules      []AlignmentRule
    violations []AlignmentViolation
    suggestions []AlignmentSuggestion
}

// AlignmentRule defines alignment rules
type AlignmentRule struct {
    TypePattern string
    MinAlignment uintptr
    MaxAlignment uintptr
    Description string
}

// AlignmentViolation represents an alignment issue
type AlignmentViolation struct {
    StructName  string
    FieldName   string
    Expected    uintptr
    Actual      uintptr
    Impact      ViolationImpact
    Severity    ViolationSeverity
}

// ViolationImpact measures the impact of alignment violations
type ViolationImpact struct {
    MemoryWaste     uintptr
    CacheEfficiency float64
    PerformanceHit  float64
}

// ViolationSeverity defines violation severity levels
type ViolationSeverity int

const (
    LowSeverity ViolationSeverity = iota
    MediumSeverity
    HighSeverity
    CriticalSeverity
)

// AlignmentSuggestion provides optimization suggestions
type AlignmentSuggestion struct {
    StructName    string
    Optimization  OptimizationType
    Description   string
    ExpectedGain  OptimizationGain
    Implementation string
    Example       string
}

// OptimizationType defines optimization types
type OptimizationType int

const (
    FieldReordering OptimizationType = iota
    StructPacking
    CacheAlignment
    MemoryPooling
    DataLocality
    PaddingReduction
)

// OptimizationGain measures expected optimization gains
type OptimizationGain struct {
    SizeReduction    uintptr
    CacheImprovement float64
    MemoryBandwidth  float64
    LatencyReduction float64
}

// LayoutOptimizer optimizes memory layouts
type LayoutOptimizer struct {
    strategies []OptimizationStrategy
    rules      []OptimizationRule
    results    map[string]*OptimizationResult
}

// OptimizationStrategy defines layout optimization strategies
type OptimizationStrategy interface {
    Analyze(info *StructureInfo) *OptimizationResult
    Apply(structDef string) (string, error)
    Estimate(info *StructureInfo) OptimizationGain
}

// OptimizationRule defines optimization rules
type OptimizationRule struct {
    Pattern     string
    Action      string
    Priority    int
    Conditions  []string
    Description string
}

// OptimizationResult contains optimization results
type OptimizationResult struct {
    OriginalSize     uintptr
    OptimizedSize    uintptr
    SizeReduction    uintptr
    FieldOrder       []string
    PaddingReduced   uintptr
    CacheEfficiency  float64
    Implementation   string
}

// CacheProfiler profiles cache behavior
type CacheProfiler struct {
    config      CacheConfig
    metrics     *CacheMetrics
    hotspots    []CacheHotspot
    missPatterns []MissPattern
}

// CacheConfig contains cache profiling configuration
type CacheConfig struct {
    L1CacheSize  int
    L2CacheSize  int
    L3CacheSize  int
    LineSize     int
    Associativity int
    EnableTracing bool
}

// CacheMetrics tracks cache performance
type CacheMetrics struct {
    L1Hits        int64
    L1Misses      int64
    L2Hits        int64
    L2Misses      int64
    L3Hits        int64
    L3Misses      int64
    CacheMissRate float64
    MemoryLatency time.Duration
    Bandwidth     float64
}

// CacheHotspot identifies cache performance hotspots
type CacheHotspot struct {
    Address     uintptr
    StructName  string
    FieldName   string
    MissRate    float64
    AccessCount int64
    Impact      CacheImpact
}

// CacheImpact measures cache performance impact
type CacheImpact struct {
    LatencyIncrease  time.Duration
    BandwidthReduction float64
    ThroughputImpact float64
}

// MissPattern identifies cache miss patterns
type MissPattern struct {
    Pattern     string
    Frequency   int64
    StructTypes []string
    Mitigation  string
}

// LayoutMetrics tracks overall layout performance
type LayoutMetrics struct {
    StructuresAnalyzed  int64
    TotalSizeReduction  uintptr
    AverageFragmentation float64
    CacheEfficiency     float64
    MemoryBandwidth     float64
    OptimizationsApplied int64
}

// NewMemoryLayoutAnalyzer creates a new memory layout analyzer
func NewMemoryLayoutAnalyzer(config LayoutConfig) *MemoryLayoutAnalyzer {
    return &MemoryLayoutAnalyzer{
        config:     config,
        structures: make(map[string]*StructureInfo),
        analyzer:   NewAlignmentAnalyzer(),
        optimizer:  NewLayoutOptimizer(),
        profiler:   NewCacheProfiler(config),
        metrics:    &LayoutMetrics{},
    }
}

// AnalyzeStructure analyzes a struct's memory layout
func (mla *MemoryLayoutAnalyzer) AnalyzeStructure(structType reflect.Type) (*StructureInfo, error) {
    if structType.Kind() != reflect.Struct {
        return nil, fmt.Errorf("type %s is not a struct", structType.Name())
    }

    info := &StructureInfo{
        Name:      structType.Name(),
        Type:      structType,
        Size:      structType.Size(),
        Alignment: uintptr(structType.Align()),
        Fields:    make([]FieldInfo, 0),
        Padding:   make([]PaddingInfo, 0),
        Hotness:   make(map[string]int64),
    }

    // Analyze fields
    if err := mla.analyzeFields(info, structType); err != nil {
        return nil, fmt.Errorf("field analysis failed: %w", err)
    }

    // Calculate padding
    mla.calculatePadding(info)

    // Analyze cache behavior
    mla.analyzeCacheBehavior(info)

    // Calculate fragmentation
    info.Fragmentation = mla.calculateFragmentation(info)

    // Store structure info
    mla.mu.Lock()
    mla.structures[info.Name] = info
    atomic.AddInt64(&mla.metrics.StructuresAnalyzed, 1)
    mla.mu.Unlock()

    return info, nil
}

// analyzeFields analyzes struct fields
func (mla *MemoryLayoutAnalyzer) analyzeFields(info *StructureInfo, structType reflect.Type) error {
    for i := 0; i < structType.NumField(); i++ {
        field := structType.Field(i)

        fieldInfo := FieldInfo{
            Name:       field.Name,
            Type:       field.Type,
            Size:       field.Type.Size(),
            Offset:     field.Offset,
            Alignment:  uintptr(field.Type.Align()),
            Tag:        string(field.Tag),
            IsExported: field.PkgPath == "",
            IsPointer:  field.Type.Kind() == reflect.Ptr,
        }

        info.Fields = append(info.Fields, fieldInfo)
    }

    return nil
}

// calculatePadding calculates padding bytes in the struct
func (mla *MemoryLayoutAnalyzer) calculatePadding(info *StructureInfo) {
    if len(info.Fields) == 0 {
        return
    }

    // Sort fields by offset
    fields := make([]FieldInfo, len(info.Fields))
    copy(fields, info.Fields)
    sort.Slice(fields, func(i, j int) bool {
        return fields[i].Offset < fields[j].Offset
    })

    currentOffset := uintptr(0)

    for i, field := range fields {
        // Check for padding before field
        if field.Offset > currentOffset {
            padding := PaddingInfo{
                Offset: currentOffset,
                Size:   field.Offset - currentOffset,
                Reason: "alignment",
            }
            info.Padding = append(info.Padding, padding)
        }

        currentOffset = field.Offset + field.Size

        // Check for padding at end of struct
        if i == len(fields)-1 && currentOffset < info.Size {
            padding := PaddingInfo{
                Offset: currentOffset,
                Size:   info.Size - currentOffset,
                Reason: "struct_alignment",
            }
            info.Padding = append(info.Padding, padding)
        }
    }
}

// analyzeCacheBehavior analyzes cache behavior of the structure
func (mla *MemoryLayoutAnalyzer) analyzeCacheBehavior(info *StructureInfo) {
    cacheLineSize := uintptr(mla.config.CacheLineSize)
    if cacheLineSize == 0 {
        cacheLineSize = 64 // Default cache line size
    }

    // Calculate number of cache lines
    info.CacheLines = int((info.Size + cacheLineSize - 1) / cacheLineSize)

    // Analyze field distribution across cache lines
    for i, field := range info.Fields {
        fieldStart := field.Offset
        fieldEnd := field.Offset + field.Size

        startCacheLine := fieldStart / cacheLineSize
        endCacheLine := (fieldEnd - 1) / cacheLineSize

        // Field spans multiple cache lines
        if startCacheLine != endCacheLine {
            info.Fields[i].AccessFreq = -1 // Mark as potentially problematic
        }
    }
}

// calculateFragmentation calculates memory fragmentation
func (mla *MemoryLayoutAnalyzer) calculateFragmentation(info *StructureInfo) float64 {
    totalPadding := uintptr(0)
    for _, padding := range info.Padding {
        totalPadding += padding.Size
    }

    if info.Size == 0 {
        return 0
    }

    return float64(totalPadding) / float64(info.Size)
}

// NewAlignmentAnalyzer creates a new alignment analyzer
func NewAlignmentAnalyzer() *AlignmentAnalyzer {
    analyzer := &AlignmentAnalyzer{
        rules:       make([]AlignmentRule, 0),
        violations:  make([]AlignmentViolation, 0),
        suggestions: make([]AlignmentSuggestion, 0),
    }

    // Initialize alignment rules
    analyzer.initializeRules()

    return analyzer
}

// initializeRules initializes alignment rules
func (aa *AlignmentAnalyzer) initializeRules() {
    // Common alignment rules
    aa.rules = append(aa.rules, AlignmentRule{
        TypePattern:  "int64|uint64|float64",
        MinAlignment: 8,
        MaxAlignment: 8,
        Description:  "64-bit types should be 8-byte aligned",
    })

    aa.rules = append(aa.rules, AlignmentRule{
        TypePattern:  "int32|uint32|float32",
        MinAlignment: 4,
        MaxAlignment: 4,
        Description:  "32-bit types should be 4-byte aligned",
    })

    aa.rules = append(aa.rules, AlignmentRule{
        TypePattern:  "int16|uint16",
        MinAlignment: 2,
        MaxAlignment: 2,
        Description:  "16-bit types should be 2-byte aligned",
    })

    aa.rules = append(aa.rules, AlignmentRule{
        TypePattern:  "\\*",
        MinAlignment: 8,
        MaxAlignment: 8,
        Description:  "Pointers should be 8-byte aligned on 64-bit systems",
    })
}

// AnalyzeAlignment analyzes struct alignment
func (aa *AlignmentAnalyzer) AnalyzeAlignment(info *StructureInfo) error {
    aa.violations = aa.violations[:0] // Clear previous violations

    for _, field := range info.Fields {
        if violation := aa.checkFieldAlignment(info.Name, field); violation != nil {
            aa.violations = append(aa.violations, *violation)
        }
    }

    // Generate suggestions based on violations
    aa.generateSuggestions(info)

    return nil
}

// checkFieldAlignment checks if a field violates alignment rules
func (aa *AlignmentAnalyzer) checkFieldAlignment(structName string, field FieldInfo) *AlignmentViolation {
    expectedAlignment := aa.getExpectedAlignment(field.Type)

    if expectedAlignment > 0 && field.Offset%expectedAlignment != 0 {
        impact := ViolationImpact{
            MemoryWaste:     expectedAlignment - (field.Offset % expectedAlignment),
            CacheEfficiency: 0.9, // Simplified calculation
            PerformanceHit:  0.1,  // Simplified calculation
        }

        return &AlignmentViolation{
            StructName: structName,
            FieldName:  field.Name,
            Expected:   expectedAlignment,
            Actual:     field.Offset % expectedAlignment,
            Impact:     impact,
            Severity:   aa.calculateSeverity(impact),
        }
    }

    return nil
}

// getExpectedAlignment returns expected alignment for a type
func (aa *AlignmentAnalyzer) getExpectedAlignment(t reflect.Type) uintptr {
    switch t.Kind() {
    case reflect.Int64, reflect.Uint64, reflect.Float64:
        return 8
    case reflect.Int32, reflect.Uint32, reflect.Float32:
        return 4
    case reflect.Int16, reflect.Uint16:
        return 2
    case reflect.Ptr, reflect.UnsafePointer:
        return 8 // Assuming 64-bit system
    case reflect.Struct:
        return uintptr(t.Align())
    default:
        return 1
    }
}

// calculateSeverity calculates violation severity
func (aa *AlignmentAnalyzer) calculateSeverity(impact ViolationImpact) ViolationSeverity {
    if impact.PerformanceHit > 0.2 {
        return CriticalSeverity
    } else if impact.PerformanceHit > 0.1 {
        return HighSeverity
    } else if impact.PerformanceHit > 0.05 {
        return MediumSeverity
    }
    return LowSeverity
}

// generateSuggestions generates optimization suggestions
func (aa *AlignmentAnalyzer) generateSuggestions(info *StructureInfo) {
    aa.suggestions = aa.suggestions[:0] // Clear previous suggestions

    // Suggest field reordering if there are violations
    if len(aa.violations) > 0 {
        suggestion := AlignmentSuggestion{
            StructName:   info.Name,
            Optimization: FieldReordering,
            Description:  "Reorder fields to reduce padding and improve alignment",
            ExpectedGain: aa.calculateReorderingGain(info),
            Implementation: "Order fields by size (largest first) or by access pattern",
            Example:      aa.generateReorderingExample(info),
        }
        aa.suggestions = append(aa.suggestions, suggestion)
    }

    // Suggest struct packing if fragmentation is high
    if info.Fragmentation > 0.2 {
        suggestion := AlignmentSuggestion{
            StructName:   info.Name,
            Optimization: StructPacking,
            Description:  "Use struct tags or bit fields to reduce memory usage",
            ExpectedGain: aa.calculatePackingGain(info),
            Implementation: "Use smaller types or bit fields where appropriate",
            Example:      "type OptimizedStruct struct { flags uint8; id uint16; data uint32 }",
        }
        aa.suggestions = append(aa.suggestions, suggestion)
    }
}

// calculateReorderingGain calculates expected gain from field reordering
func (aa *AlignmentAnalyzer) calculateReorderingGain(info *StructureInfo) OptimizationGain {
    // Simulate optimal field ordering
    optimizedSize := aa.calculateOptimalSize(info)

    return OptimizationGain{
        SizeReduction:    info.Size - optimizedSize,
        CacheImprovement: 0.15, // Estimated
        MemoryBandwidth:  0.1,  // Estimated
        LatencyReduction: 0.05, // Estimated
    }
}

// calculateOptimalSize calculates optimal struct size with field reordering
func (aa *AlignmentAnalyzer) calculateOptimalSize(info *StructureInfo) uintptr {
    // Sort fields by alignment requirements (largest first)
    fields := make([]FieldInfo, len(info.Fields))
    copy(fields, info.Fields)

    sort.Slice(fields, func(i, j int) bool {
        return fields[i].Alignment > fields[j].Alignment
    })

    currentOffset := uintptr(0)
    maxAlignment := uintptr(1)

    for _, field := range fields {
        // Align field
        if field.Alignment > maxAlignment {
            maxAlignment = field.Alignment
        }

        aligned := (currentOffset + field.Alignment - 1) &^ (field.Alignment - 1)
        currentOffset = aligned + field.Size
    }

    // Align struct to maximum field alignment
    finalSize := (currentOffset + maxAlignment - 1) &^ (maxAlignment - 1)

    return finalSize
}

// calculatePackingGain calculates expected gain from struct packing
func (aa *AlignmentAnalyzer) calculatePackingGain(info *StructureInfo) OptimizationGain {
    // Estimate packing savings based on current fragmentation
    estimatedSaving := uintptr(float64(info.Size) * info.Fragmentation * 0.5)

    return OptimizationGain{
        SizeReduction:    estimatedSaving,
        CacheImprovement: 0.1,
        MemoryBandwidth:  0.05,
        LatencyReduction: 0.02,
    }
}

// generateReorderingExample generates a field reordering example
func (aa *AlignmentAnalyzer) generateReorderingExample(info *StructureInfo) string {
    // Sort fields by alignment (largest first)
    fields := make([]FieldInfo, len(info.Fields))
    copy(fields, info.Fields)

    sort.Slice(fields, func(i, j int) bool {
        return fields[i].Alignment > fields[j].Alignment
    })

    example := fmt.Sprintf("type %s struct {\n", info.Name)
    for _, field := range fields {
        example += fmt.Sprintf("    %s %s\n", field.Name, field.Type.String())
    }
    example += "}"

    return example
}

// NewLayoutOptimizer creates a new layout optimizer
func NewLayoutOptimizer() *LayoutOptimizer {
    optimizer := &LayoutOptimizer{
        strategies: make([]OptimizationStrategy, 0),
        rules:      make([]OptimizationRule, 0),
        results:    make(map[string]*OptimizationResult),
    }

    // Initialize optimization strategies
    optimizer.initializeStrategies()

    return optimizer
}

// initializeStrategies initializes optimization strategies
func (lo *LayoutOptimizer) initializeStrategies() {
    lo.strategies = append(lo.strategies, &FieldReorderingStrategy{})
    lo.strategies = append(lo.strategies, &CacheAlignmentStrategy{})
    lo.strategies = append(lo.strategies, &PaddingReductionStrategy{})
}

// OptimizeLayout optimizes struct layout
func (lo *LayoutOptimizer) OptimizeLayout(info *StructureInfo) (*OptimizationResult, error) {
    var bestResult *OptimizationResult
    var bestSavings uintptr

    // Try each optimization strategy
    for _, strategy := range lo.strategies {
        result := strategy.Analyze(info)
        if result != nil && result.SizeReduction > bestSavings {
            bestResult = result
            bestSavings = result.SizeReduction
        }
    }

    if bestResult != nil {
        lo.results[info.Name] = bestResult
    }

    return bestResult, nil
}

// FieldReorderingStrategy optimizes field ordering
type FieldReorderingStrategy struct{}

// Analyze analyzes field reordering opportunities
func (frs *FieldReorderingStrategy) Analyze(info *StructureInfo) *OptimizationResult {
    // Calculate optimal field order
    optimizedFields := frs.calculateOptimalOrder(info.Fields)
    optimizedSize := frs.calculateSizeWithOrder(optimizedFields)

    if optimizedSize >= info.Size {
        return nil // No improvement
    }

    fieldOrder := make([]string, len(optimizedFields))
    for i, field := range optimizedFields {
        fieldOrder[i] = field.Name
    }

    return &OptimizationResult{
        OriginalSize:    info.Size,
        OptimizedSize:   optimizedSize,
        SizeReduction:   info.Size - optimizedSize,
        FieldOrder:      fieldOrder,
        CacheEfficiency: 0.15, // Estimated improvement
        Implementation:  frs.generateImplementation(optimizedFields, info.Name),
    }
}

// calculateOptimalOrder calculates optimal field ordering
func (frs *FieldReorderingStrategy) calculateOptimalOrder(fields []FieldInfo) []FieldInfo {
    // Sort by alignment requirements (largest first), then by size
    optimized := make([]FieldInfo, len(fields))
    copy(optimized, fields)

    sort.Slice(optimized, func(i, j int) bool {
        if optimized[i].Alignment != optimized[j].Alignment {
            return optimized[i].Alignment > optimized[j].Alignment
        }
        return optimized[i].Size > optimized[j].Size
    })

    return optimized
}

// calculateSizeWithOrder calculates struct size with given field order
func (frs *FieldReorderingStrategy) calculateSizeWithOrder(fields []FieldInfo) uintptr {
    currentOffset := uintptr(0)
    maxAlignment := uintptr(1)

    for _, field := range fields {
        if field.Alignment > maxAlignment {
            maxAlignment = field.Alignment
        }

        // Align field
        aligned := (currentOffset + field.Alignment - 1) &^ (field.Alignment - 1)
        currentOffset = aligned + field.Size
    }

    // Align struct to maximum field alignment
    finalSize := (currentOffset + maxAlignment - 1) &^ (maxAlignment - 1)
    return finalSize
}

// generateImplementation generates optimized struct implementation
func (frs *FieldReorderingStrategy) generateImplementation(fields []FieldInfo, structName string) string {
    impl := fmt.Sprintf("type %s struct {\n", structName)
    for _, field := range fields {
        impl += fmt.Sprintf("    %s %s", field.Name, field.Type.String())
        if field.Tag != "" {
            impl += fmt.Sprintf(" `%s`", field.Tag)
        }
        impl += "\n"
    }
    impl += "}"
    return impl
}

// Apply applies field reordering optimization
func (frs *FieldReorderingStrategy) Apply(structDef string) (string, error) {
    // This would implement actual code transformation
    return structDef, nil
}

// Estimate estimates optimization impact
func (frs *FieldReorderingStrategy) Estimate(info *StructureInfo) OptimizationGain {
    optimizedFields := frs.calculateOptimalOrder(info.Fields)
    optimizedSize := frs.calculateSizeWithOrder(optimizedFields)

    return OptimizationGain{
        SizeReduction:    info.Size - optimizedSize,
        CacheImprovement: 0.15,
        MemoryBandwidth:  0.1,
        LatencyReduction: 0.05,
    }
}

// CacheAlignmentStrategy optimizes for cache alignment
type CacheAlignmentStrategy struct{}

// Analyze analyzes cache alignment opportunities
func (cas *CacheAlignmentStrategy) Analyze(info *StructureInfo) *OptimizationResult {
    cacheLineSize := uintptr(64) // Typical cache line size

    // Check if struct would benefit from cache line alignment
    if info.Size <= cacheLineSize && info.CacheLines > 1 {
        // Struct spans multiple cache lines but is small enough to fit in one
        paddedSize := cacheLineSize

        return &OptimizationResult{
            OriginalSize:    info.Size,
            OptimizedSize:   paddedSize,
            SizeReduction:   0, // Size increases but cache efficiency improves
            CacheEfficiency: 0.3, // Significant cache improvement
            Implementation:  cas.generateCacheAlignedStruct(info, cacheLineSize),
        }
    }

    return nil
}

// generateCacheAlignedStruct generates cache-aligned struct
func (cas *CacheAlignmentStrategy) generateCacheAlignedStruct(info *StructureInfo, cacheLineSize uintptr) string {
    return fmt.Sprintf("type %s struct {\n    // Cache-aligned struct\n    %s\n} // Size: %d bytes, Cache-aligned\n",
        info.Name, "/* fields */", cacheLineSize)
}

// Apply applies cache alignment optimization
func (cas *CacheAlignmentStrategy) Apply(structDef string) (string, error) {
    return structDef, nil
}

// Estimate estimates cache alignment impact
func (cas *CacheAlignmentStrategy) Estimate(info *StructureInfo) OptimizationGain {
    return OptimizationGain{
        SizeReduction:    0, // May increase size
        CacheImprovement: 0.3,
        MemoryBandwidth:  0.2,
        LatencyReduction: 0.15,
    }
}

// PaddingReductionStrategy reduces padding
type PaddingReductionStrategy struct{}

// Analyze analyzes padding reduction opportunities
func (prs *PaddingReductionStrategy) Analyze(info *StructureInfo) *OptimizationResult {
    totalPadding := uintptr(0)
    for _, padding := range info.Padding {
        totalPadding += padding.Size
    }

    if totalPadding == 0 {
        return nil // No padding to reduce
    }

    // Estimate achievable padding reduction
    achievableReduction := totalPadding * 70 / 100 // Assume 70% reduction possible

    return &OptimizationResult{
        OriginalSize:    info.Size,
        OptimizedSize:   info.Size - achievableReduction,
        SizeReduction:   achievableReduction,
        PaddingReduced:  achievableReduction,
        CacheEfficiency: 0.1,
        Implementation:  "Reorder fields and use appropriate types",
    }
}

// Apply applies padding reduction optimization
func (prs *PaddingReductionStrategy) Apply(structDef string) (string, error) {
    return structDef, nil
}

// Estimate estimates padding reduction impact
func (prs *PaddingReductionStrategy) Estimate(info *StructureInfo) OptimizationGain {
    totalPadding := uintptr(0)
    for _, padding := range info.Padding {
        totalPadding += padding.Size
    }

    return OptimizationGain{
        SizeReduction:    totalPadding * 70 / 100,
        CacheImprovement: 0.1,
        MemoryBandwidth:  0.05,
        LatencyReduction: 0.02,
    }
}

// NewCacheProfiler creates a new cache profiler
func NewCacheProfiler(config LayoutConfig) *CacheProfiler {
    cacheConfig := CacheConfig{
        L1CacheSize:   32 * 1024,  // 32KB
        L2CacheSize:   256 * 1024, // 256KB
        L3CacheSize:   8 * 1024 * 1024, // 8MB
        LineSize:      64,
        Associativity: 8,
        EnableTracing: config.EnableProfiling,
    }

    return &CacheProfiler{
        config:       cacheConfig,
        metrics:      &CacheMetrics{},
        hotspots:     make([]CacheHotspot, 0),
        missPatterns: make([]MissPattern, 0),
    }
}

// ProfileCacheBehavior profiles cache behavior for a structure
func (cp *CacheProfiler) ProfileCacheBehavior(info *StructureInfo) error {
    // Simulate cache behavior analysis
    cp.analyzeCacheLineUsage(info)
    cp.identifyHotspots(info)
    cp.detectMissPatterns(info)

    return nil
}

// analyzeCacheLineUsage analyzes cache line usage
func (cp *CacheProfiler) analyzeCacheLineUsage(info *StructureInfo) {
    cacheLineSize := uintptr(cp.config.LineSize)

    for _, field := range info.Fields {
        fieldStart := field.Offset
        fieldEnd := field.Offset + field.Size

        startLine := fieldStart / cacheLineSize
        endLine := (fieldEnd - 1) / cacheLineSize

        if startLine != endLine {
            // Field spans multiple cache lines - potential hotspot
            hotspot := CacheHotspot{
                Address:    fieldStart,
                StructName: info.Name,
                FieldName:  field.Name,
                MissRate:   0.2, // Estimated
                AccessCount: 1000, // Estimated
                Impact: CacheImpact{
                    LatencyIncrease:    100 * time.Nanosecond,
                    BandwidthReduction: 0.15,
                    ThroughputImpact:   0.1,
                },
            }
            cp.hotspots = append(cp.hotspots, hotspot)
        }
    }
}

// identifyHotspots identifies cache performance hotspots
func (cp *CacheProfiler) identifyHotspots(info *StructureInfo) {
    // Analyze access patterns and identify frequently accessed fields
    // that may cause cache issues

    for _, field := range info.Fields {
        if field.AccessFreq > 1000 { // High frequency access
            hotspot := CacheHotspot{
                Address:     field.Offset,
                StructName:  info.Name,
                FieldName:   field.Name,
                MissRate:    0.1, // Estimated
                AccessCount: field.AccessFreq,
                Impact: CacheImpact{
                    LatencyIncrease:    50 * time.Nanosecond,
                    BandwidthReduction: 0.05,
                    ThroughputImpact:   0.03,
                },
            }
            cp.hotspots = append(cp.hotspots, hotspot)
        }
    }
}

// detectMissPatterns detects cache miss patterns
func (cp *CacheProfiler) detectMissPatterns(info *StructureInfo) {
    // Analyze struct layout for common miss patterns

    if info.CacheLines > 2 {
        pattern := MissPattern{
            Pattern:     "large_struct",
            Frequency:   100,
            StructTypes: []string{info.Name},
            Mitigation:  "Split large struct into smaller, frequently-accessed parts",
        }
        cp.missPatterns = append(cp.missPatterns, pattern)
    }

    if info.Fragmentation > 0.3 {
        pattern := MissPattern{
            Pattern:     "fragmented_layout",
            Frequency:   50,
            StructTypes: []string{info.Name},
            Mitigation:  "Reorder fields to reduce padding and improve locality",
        }
        cp.missPatterns = append(cp.missPatterns, pattern)
    }
}

// GetOptimizationSummary returns a summary of optimization opportunities
func (mla *MemoryLayoutAnalyzer) GetOptimizationSummary() *OptimizationSummary {
    mla.mu.RLock()
    defer mla.mu.RUnlock()

    summary := &OptimizationSummary{
        TotalStructures:    len(mla.structures),
        OptimizationGains:  make(map[string]OptimizationGain),
        Suggestions:        make([]AlignmentSuggestion, 0),
        CacheHotspots:      len(mla.profiler.hotspots),
        TotalSizeReduction: 0,
    }

    for name, info := range mla.structures {
        if result, err := mla.optimizer.OptimizeLayout(info); err == nil && result != nil {
            summary.OptimizationGains[name] = OptimizationGain{
                SizeReduction:    result.SizeReduction,
                CacheImprovement: result.CacheEfficiency,
            }
            summary.TotalSizeReduction += result.SizeReduction
        }

        // Add analyzer suggestions
        if err := mla.analyzer.AnalyzeAlignment(info); err == nil {
            summary.Suggestions = append(summary.Suggestions, mla.analyzer.suggestions...)
        }
    }

    return summary
}

// OptimizationSummary contains optimization summary
type OptimizationSummary struct {
    TotalStructures    int
    OptimizationGains  map[string]OptimizationGain
    Suggestions        []AlignmentSuggestion
    CacheHotspots      int
    TotalSizeReduction uintptr
}

// Example usage
func ExampleMemoryLayoutAnalysis() {
    config := LayoutConfig{
        TargetArch:       "amd64",
        CacheLineSize:    64,
        PageSize:         4096,
        EnableProfiling:  true,
        OptimizeForCache: true,
        OptimizeForSize:  true,
        AnalyzeDepth:     3,
    }

    analyzer := NewMemoryLayoutAnalyzer(config)

    // Example struct to analyze
    type ExampleStruct struct {
        A int8   // 1 byte
        B int64  // 8 bytes - will cause padding after A
        C int16  // 2 bytes
        D int32  // 4 bytes
        E int8   // 1 byte - will cause padding at end
    }

    structType := reflect.TypeOf(ExampleStruct{})
    info, err := analyzer.AnalyzeStructure(structType)
    if err != nil {
        fmt.Printf("Analysis failed: %v\n", err)
        return
    }

    fmt.Printf("Original struct size: %d bytes\n", info.Size)
    fmt.Printf("Fragmentation: %.2f%%\n", info.Fragmentation*100)
    fmt.Printf("Cache lines: %d\n", info.CacheLines)

    // Get optimization result
    result, err := analyzer.optimizer.OptimizeLayout(info)
    if err == nil && result != nil {
        fmt.Printf("Optimized size: %d bytes\n", result.OptimizedSize)
        fmt.Printf("Size reduction: %d bytes\n", result.SizeReduction)
        fmt.Printf("Optimized field order: %v\n", result.FieldOrder)
    }

    // Get summary
    summary := analyzer.GetOptimizationSummary()
    fmt.Printf("Total optimization opportunities: %d\n", len(summary.OptimizationGains))
    fmt.Printf("Total size reduction: %d bytes\n", summary.TotalSizeReduction)
}

Performance Analysis

Advanced techniques for analyzing memory layout performance impact.

Cache Performance Measurement

Tools and techniques for measuring cache performance.

Memory Bandwidth Analysis

Analyzing memory bandwidth utilization and optimization.

NUMA Optimization

Optimizing data structures for NUMA architectures.

Best Practices

  1. Field Ordering: Order fields by alignment requirements (largest first)
  2. Cache Line Awareness: Design structures to fit within cache lines
  3. Hot/Cold Separation: Separate frequently and infrequently accessed fields
  4. Avoid False Sharing: Ensure independent data doesn't share cache lines
  5. Use Appropriate Types: Choose the smallest appropriate data types
  6. Consider Access Patterns: Optimize layout based on how data is accessed
  7. Profile Memory Usage: Use tools to measure actual memory behavior
  8. Test Optimizations: Benchmark before and after layout changes

Summary

Memory layout optimization is crucial for high-performance Go applications:

  1. Understanding: Know how memory alignment and padding work
  2. Analysis: Use tools to identify layout inefficiencies
  3. Optimization: Apply systematic optimization strategies
  4. Measurement: Profile cache behavior and memory usage
  5. Validation: Benchmark optimization impact

These techniques enable developers to create memory-efficient data structures that maximize CPU cache utilization and minimize memory footprint.

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