rustorch 0.6.29

//! GPU Memory Management Integration Module
//! 
//! Integrates GPU memory operations with the enhanced memory management system,
//! providing unified memory allocation, transfer optimization, and pressure management.

use crate::error::{RusTorchError, RusTorchResult};
use crate::memory::{
    MemoryPool, pressure_monitor::PressureMonitor, 
    AllocationStrategy, PressureLevel
};
use crate::tensor::Tensor;
use std::collections::{HashMap, VecDeque};
use std::sync::{Arc, Mutex, RwLock};
use std::time::{Duration, Instant};

/// Unified memory type for CPU/GPU transfers
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum MemoryLocation {
    /// Host (CPU) memory
    Host,
    /// Device (GPU) memory
    Device(usize),
    /// Unified memory (accessible by both)
    Unified,
    /// Pinned host memory (for fast transfers)
    PinnedHost,
}

/// Memory transfer direction
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TransferDirection {
    /// Host to Device
    HostToDevice,
    /// Device to Host
    DeviceToHost,
    /// Device to Device (same GPU)
    DeviceToDevice,
    /// Peer to Peer (different GPUs)
    PeerToPeer(usize, usize),
}

/// GPU memory allocator with integration to memory pool
pub struct GpuMemoryAllocator {
    /// Device ID
    device_id: usize,
    /// Total device memory
    total_memory: usize,
    /// Available device memory
    available_memory: Arc<RwLock<usize>>,
    /// Memory pool integration
    memory_pool: Arc<MemoryPool<f32>>,
    /// Allocation map
    allocations: Arc<RwLock<HashMap<usize, GpuAllocation>>>,
    /// Transfer optimizer
    transfer_optimizer: Arc<TransferOptimizer>,
    /// Pinned memory cache
    pinned_cache: Arc<PinnedMemoryCache>,
}

/// GPU memory allocation record
#[derive(Debug, Clone)]
pub struct GpuAllocation {
    /// Allocation ID
    pub id: usize,
    /// Device pointer
    pub device_ptr: usize,
    /// Size in bytes
    pub size: usize,
    /// Memory location
    pub location: MemoryLocation,
    /// Allocation timestamp
    pub allocated_at: Instant,
    /// Last accessed timestamp
    pub last_accessed: Instant,
    /// Reference count
    pub ref_count: usize,
    /// Is pinned
    pub is_pinned: bool,
}

/// Transfer optimization engine
pub struct TransferOptimizer {
    /// Transfer queue
    transfer_queue: Mutex<VecDeque<TransferRequest>>,
    /// Transfer statistics
    statistics: RwLock<TransferStatistics>,
    /// Optimization configuration
    config: TransferConfig,
    /// Bandwidth estimator
    bandwidth_estimator: BandwidthEstimator,
    /// Prefetch predictor
    prefetch_predictor: PrefetchPredictor,
}

/// Transfer request
#[derive(Debug, Clone)]
pub struct TransferRequest {
    /// Request ID
    pub id: u64,
    /// Source location
    pub source: MemoryLocation,
    /// Destination location
    pub destination: MemoryLocation,
    /// Data size
    pub size: usize,
    /// Priority
    pub priority: TransferPriority,
    /// Async flag
    pub is_async: bool,
    /// Completion callback
    pub callback: Option<Arc<dyn Fn() + Send + Sync>>,
}

/// Transfer priority levels
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum TransferPriority {
    /// Immediate transfer (blocking)
    Immediate = 0,
    /// High priority
    High = 1,
    /// Normal priority
    Normal = 2,
    /// Low priority (background)
    Low = 3,
}

/// Transfer statistics
#[derive(Debug, Default)]
pub struct TransferStatistics {
    /// Total transfers
    pub total_transfers: u64,
    /// Total bytes transferred
    pub total_bytes: usize,
    /// Average transfer time
    pub avg_transfer_time: Duration,
    /// Peak bandwidth achieved
    pub peak_bandwidth: f64,
    /// Transfer patterns
    pub patterns: HashMap<TransferDirection, u64>,
}

/// Transfer configuration
#[derive(Debug, Clone)]
pub struct TransferConfig {
    /// Enable async transfers
    pub async_transfers: bool,
    /// Enable transfer compression
    pub compression: bool,
    /// Enable transfer coalescing
    pub coalescing: bool,
    /// Maximum coalescing window
    pub coalescing_window: Duration,
    /// Prefetch distance
    pub prefetch_distance: usize,
}

/// Bandwidth estimator for transfer optimization
pub struct BandwidthEstimator {
    /// Historical bandwidth measurements
    measurements: VecDeque<BandwidthMeasurement>,
    /// Maximum history size
    max_history: usize,
    /// Current estimate
    current_estimate: f64,
}

/// Bandwidth measurement
#[derive(Debug, Clone)]
pub struct BandwidthMeasurement {
    /// Transfer direction
    pub direction: TransferDirection,
    /// Bytes transferred
    pub bytes: usize,
    /// Transfer time
    pub duration: Duration,
    /// Achieved bandwidth
    pub bandwidth: f64,
    /// Timestamp
    pub timestamp: Instant,
}

/// Prefetch predictor for proactive transfers
pub struct PrefetchPredictor {
    /// Access pattern history
    access_history: VecDeque<AccessPattern>,
    /// Prediction model
    prediction_model: PredictionModel,
    /// Prefetch accuracy
    accuracy: f64,
}

/// Access pattern record
#[derive(Debug, Clone)]
pub struct AccessPattern {
    /// Tensor ID
    pub tensor_id: usize,
    /// Access timestamp
    pub timestamp: Instant,
    /// Access type
    pub access_type: AccessType,
    /// Memory location
    pub location: MemoryLocation,
}

/// Access type
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum AccessType {
    /// Read access
    Read,
    /// Write access
    Write,
    /// Read-Modify-Write
    ReadModifyWrite,
}

/// Prediction model for prefetching
#[derive(Debug)]
pub struct PredictionModel {
    /// Pattern detection threshold
    pub threshold: f64,
    /// Lookahead distance
    pub lookahead: usize,
    /// Confidence level
    pub confidence: f64,
}

/// Pinned memory cache for fast transfers
pub struct PinnedMemoryCache {
    /// Cached pinned allocations
    cache: RwLock<HashMap<usize, PinnedAllocation>>,
    /// Total pinned memory limit
    max_pinned_memory: usize,
    /// Current pinned memory usage
    current_usage: Arc<RwLock<usize>>,
    /// LRU eviction queue
    lru_queue: Mutex<VecDeque<usize>>,
}

/// Pinned memory allocation
#[derive(Debug, Clone)]
pub struct PinnedAllocation {
    /// Host pointer
    pub host_ptr: usize,
    /// Size in bytes
    pub size: usize,
    /// Is in use
    pub in_use: bool,
    /// Last used timestamp
    pub last_used: Instant,
}

/// Unified memory manager for CPU-GPU coherence
pub struct UnifiedMemoryManager {
    /// Unified allocations
    allocations: Arc<RwLock<HashMap<usize, UnifiedAllocation>>>,
    /// Coherence protocol
    coherence_protocol: CoherenceProtocol,
    /// Migration policy
    migration_policy: MigrationPolicy,
    /// Page fault handler
    fault_handler: Arc<PageFaultHandler>,
}

/// Unified memory allocation
#[derive(Debug, Clone)]
pub struct UnifiedAllocation {
    /// Allocation ID
    pub id: usize,
    /// Virtual address
    pub virtual_addr: usize,
    /// Size in bytes
    pub size: usize,
    /// Current residency
    pub residency: MemoryLocation,
    /// Access counters
    pub access_counters: AccessCounters,
    /// Migration history
    pub migration_history: Vec<MigrationEvent>,
}

/// Access counters for migration decisions
#[derive(Debug, Clone, Default)]
pub struct AccessCounters {
    /// CPU access count
    pub cpu_accesses: u64,
    /// GPU access count
    pub gpu_accesses: u64,
    /// Last CPU access
    pub last_cpu_access: Option<Instant>,
    /// Last GPU access
    pub last_gpu_access: Option<Instant>,
}

/// Migration event record
#[derive(Debug, Clone)]
pub struct MigrationEvent {
    /// Migration timestamp
    pub timestamp: Instant,
    /// Source location
    pub from: MemoryLocation,
    /// Destination location
    pub to: MemoryLocation,
    /// Migration reason
    pub reason: MigrationReason,
    /// Bytes migrated
    pub bytes: usize,
}

/// Migration reasons
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum MigrationReason {
    /// Page fault triggered
    PageFault,
    /// Proactive prefetch
    Prefetch,
    /// Memory pressure
    Pressure,
    /// Access pattern change
    AccessPattern,
    /// Manual migration
    Manual,
}

/// Coherence protocol for unified memory
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum CoherenceProtocol {
    /// Write-through protocol
    WriteThrough,
    /// Write-back protocol
    WriteBack,
    /// Write-invalidate protocol
    WriteInvalidate,
}

/// Migration policy for unified memory
#[derive(Debug, Clone)]
pub struct MigrationPolicy {
    /// Migration threshold
    pub threshold: f64,
    /// Eager migration
    pub eager_migration: bool,
    /// Migration granularity
    pub granularity: MigrationGranularity,
}

/// Migration granularity
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum MigrationGranularity {
    /// Page-level migration
    Page,
    /// Block-level migration
    Block(usize),
    /// Full allocation migration
    Full,
}

/// Page fault handler for unified memory
pub struct PageFaultHandler {
    /// Fault statistics
    fault_stats: RwLock<FaultStatistics>,
    /// Fault resolution strategy
    resolution_strategy: ResolutionStrategy,
}

/// Fault statistics
#[derive(Debug, Default)]
pub struct FaultStatistics {
    /// Total faults
    pub total_faults: u64,
    /// CPU faults
    pub cpu_faults: u64,
    /// GPU faults
    pub gpu_faults: u64,
    /// Average resolution time
    pub avg_resolution_time: Duration,
}

/// Fault resolution strategy
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ResolutionStrategy {
    /// Immediate migration
    Immediate,
    /// Deferred migration
    Deferred,
    /// Replicated access
    Replicated,
}

impl GpuMemoryAllocator {
    /// Create new GPU memory allocator
    pub fn new(device_id: usize, total_memory: usize, memory_pool: Arc<MemoryPool<f32>>) -> Self {
        Self {
            device_id,
            total_memory,
            available_memory: Arc::new(RwLock::new(total_memory)),
            memory_pool,
            allocations: Arc::new(RwLock::new(HashMap::new())),
            transfer_optimizer: Arc::new(TransferOptimizer::new(TransferConfig::default())),
            pinned_cache: Arc::new(PinnedMemoryCache::new(1024 * 1024 * 100)), // 100MB pinned cache
        }
    }

    /// Allocate GPU memory
    pub fn allocate(&self, size: usize) -> RusTorchResult<GpuAllocation> {
        // Check available memory
        let mut available = self.available_memory.write().unwrap();
        if *available < size {
            // Try to free memory through pool
            self.memory_pool.trigger_gc();
            
            // Re-check
            if *available < size {
                return Err(RusTorchError::OutOfMemory(format!(
                    "Cannot allocate {} bytes on GPU {}", size, self.device_id
                )));
            }
        }

        // Allocate memory (platform-specific)
        let device_ptr = self.allocate_device_memory(size)?;
        
        // Update available memory
        *available -= size;

        // Create allocation record
        let allocation = GpuAllocation {
            id: self.generate_allocation_id(),
            device_ptr,
            size,
            location: MemoryLocation::Device(self.device_id),
            allocated_at: Instant::now(),
            last_accessed: Instant::now(),
            ref_count: 1,
            is_pinned: false,
        };

        // Store allocation
        let mut allocations = self.allocations.write().unwrap();
        allocations.insert(allocation.id, allocation.clone());

        Ok(allocation)
    }

    /// Deallocate GPU memory
    pub fn deallocate(&self, allocation_id: usize) -> RusTorchResult<()> {
        let mut allocations = self.allocations.write().unwrap();
        
        if let Some(allocation) = allocations.remove(&allocation_id) {
            // Free device memory (platform-specific)
            self.free_device_memory(allocation.device_ptr)?;
            
            // Update available memory
            let mut available = self.available_memory.write().unwrap();
            *available += allocation.size;
        }

        Ok(())
    }

    /// Transfer data between host and device
    pub fn transfer(&self, request: TransferRequest) -> RusTorchResult<()> {
        // Optimize transfer through optimizer
        self.transfer_optimizer.optimize_and_execute(request)
    }

    /// Allocate pinned host memory
    pub fn allocate_pinned(&self, size: usize) -> RusTorchResult<PinnedAllocation> {
        self.pinned_cache.allocate(size)
    }

    /// Platform-specific device memory allocation
    fn allocate_device_memory(&self, size: usize) -> RusTorchResult<usize> {
        // Platform-specific implementation (CUDA, Metal, etc.)
        Ok(0) // Placeholder
    }

    /// Platform-specific device memory deallocation
    fn free_device_memory(&self, ptr: usize) -> RusTorchResult<()> {
        // Platform-specific implementation
        Ok(())
    }

    /// Generate unique allocation ID
    fn generate_allocation_id(&self) -> usize {
        use std::sync::atomic::{AtomicUsize, Ordering};
        static COUNTER: AtomicUsize = AtomicUsize::new(0);
        COUNTER.fetch_add(1, Ordering::SeqCst)
    }

    /// Get memory usage statistics
    pub fn memory_stats(&self) -> GpuMemoryStats {
        let available = *self.available_memory.read().unwrap();
        let allocations = self.allocations.read().unwrap();
        
        GpuMemoryStats {
            device_id: self.device_id,
            total_memory: self.total_memory,
            available_memory: available,
            used_memory: self.total_memory - available,
            allocation_count: allocations.len(),
            fragmentation: self.calculate_fragmentation(),
        }
    }

    /// Calculate memory fragmentation
    fn calculate_fragmentation(&self) -> f64 {
        // Calculate fragmentation metric
        0.0 // Placeholder
    }
}

/// GPU memory statistics
#[derive(Debug, Clone)]
pub struct GpuMemoryStats {
    /// Device ID
    pub device_id: usize,
    /// Total memory
    pub total_memory: usize,
    /// Available memory
    pub available_memory: usize,
    /// Used memory
    pub used_memory: usize,
    /// Number of allocations
    pub allocation_count: usize,
    /// Fragmentation percentage
    pub fragmentation: f64,
}

impl TransferOptimizer {
    /// Create new transfer optimizer
    pub fn new(config: TransferConfig) -> Self {
        Self {
            transfer_queue: Mutex::new(VecDeque::new()),
            statistics: RwLock::new(TransferStatistics::default()),
            config,
            bandwidth_estimator: BandwidthEstimator::new(),
            prefetch_predictor: PrefetchPredictor::new(),
        }
    }

    /// Optimize and execute transfer
    pub fn optimize_and_execute(&self, request: TransferRequest) -> RusTorchResult<()> {
        // Estimate bandwidth for scheduling
        let estimated_time = self.estimate_transfer_time(&request);
        
        // Check if coalescing is beneficial
        if self.config.coalescing && self.should_coalesce(&request, estimated_time) {
            self.queue_for_coalescing(request)?;
        } else {
            self.execute_transfer(request)?;
        }

        Ok(())
    }

    /// Estimate transfer time
    fn estimate_transfer_time(&self, request: &TransferRequest) -> Duration {
        let direction = self.get_transfer_direction(&request.source, &request.destination);
        let bandwidth = self.bandwidth_estimator.estimate(direction);
        
        Duration::from_secs_f64(request.size as f64 / bandwidth)
    }

    /// Check if transfer should be coalesced
    fn should_coalesce(&self, request: &TransferRequest, estimated_time: Duration) -> bool {
        request.priority == TransferPriority::Low && 
        estimated_time < self.config.coalescing_window
    }

    /// Queue transfer for coalescing
    fn queue_for_coalescing(&self, request: TransferRequest) -> RusTorchResult<()> {
        let mut queue = self.transfer_queue.lock().unwrap();
        queue.push_back(request);
        
        // Check if we should flush the queue
        if queue.len() >= 16 || self.oldest_request_age(&queue) > self.config.coalescing_window {
            self.flush_coalesced_transfers()?;
        }

        Ok(())
    }

    /// Execute transfer immediately
    fn execute_transfer(&self, request: TransferRequest) -> RusTorchResult<()> {
        let start = Instant::now();
        
        // Platform-specific transfer implementation
        self.platform_transfer(&request)?;
        
        // Update statistics
        self.update_statistics(&request, start.elapsed());
        
        // Execute callback if provided
        if let Some(callback) = &request.callback {
            callback();
        }

        Ok(())
    }

    /// Platform-specific transfer implementation
    fn platform_transfer(&self, request: &TransferRequest) -> RusTorchResult<()> {
        // Platform-specific implementation (CUDA, Metal, etc.)
        Ok(())
    }

    /// Flush coalesced transfers
    fn flush_coalesced_transfers(&self) -> RusTorchResult<()> {
        let mut queue = self.transfer_queue.lock().unwrap();
        let transfers: Vec<_> = queue.drain(..).collect();
        
        // Execute coalesced transfers
        for transfer in transfers {
            self.execute_transfer(transfer)?;
        }

        Ok(())
    }

    /// Get transfer direction
    fn get_transfer_direction(&self, source: &MemoryLocation, dest: &MemoryLocation) -> TransferDirection {
        match (source, dest) {
            (MemoryLocation::Host, MemoryLocation::Device(_)) => TransferDirection::HostToDevice,
            (MemoryLocation::Device(_), MemoryLocation::Host) => TransferDirection::DeviceToHost,
            (MemoryLocation::Device(a), MemoryLocation::Device(b)) if a == b => TransferDirection::DeviceToDevice,
            (MemoryLocation::Device(a), MemoryLocation::Device(b)) => TransferDirection::PeerToPeer(*a, *b),
            _ => TransferDirection::HostToDevice, // Default
        }
    }

    /// Get age of oldest request in queue
    fn oldest_request_age(&self, queue: &VecDeque<TransferRequest>) -> Duration {
        queue.front()
            .map(|r| Instant::now().duration_since(Instant::now())) // Placeholder
            .unwrap_or(Duration::ZERO)
    }

    /// Update transfer statistics
    fn update_statistics(&self, request: &TransferRequest, duration: Duration) {
        let mut stats = self.statistics.write().unwrap();
        
        stats.total_transfers += 1;
        stats.total_bytes += request.size;
        
        // Update average transfer time
        let total_time = stats.avg_transfer_time.as_secs_f64() * stats.total_transfers as f64;
        stats.avg_transfer_time = Duration::from_secs_f64(
            (total_time + duration.as_secs_f64()) / (stats.total_transfers as f64)
        );
        
        // Update peak bandwidth
        let bandwidth = request.size as f64 / duration.as_secs_f64();
        if bandwidth > stats.peak_bandwidth {
            stats.peak_bandwidth = bandwidth;
        }
        
        // Update pattern statistics
        let direction = self.get_transfer_direction(&request.source, &request.destination);
        *stats.patterns.entry(direction).or_insert(0) += 1;
    }
}

impl Default for TransferConfig {
    fn default() -> Self {
        Self {
            async_transfers: true,
            compression: false,
            coalescing: true,
            coalescing_window: Duration::from_millis(10),
            prefetch_distance: 2,
        }
    }
}

impl BandwidthEstimator {
    /// Create new bandwidth estimator
    pub fn new() -> Self {
        Self {
            measurements: VecDeque::new(),
            max_history: 100,
            current_estimate: 10e9, // 10 GB/s default
        }
    }

    /// Estimate bandwidth for direction
    pub fn estimate(&self, direction: TransferDirection) -> f64 {
        // Find recent measurements for this direction
        let recent: Vec<_> = self.measurements.iter()
            .filter(|m| m.direction == direction)
            .take(10)
            .collect();
        
        if recent.is_empty() {
            self.current_estimate
        } else {
            // Weighted average with recency bias
            let mut total_weight = 0.0;
            let mut weighted_sum = 0.0;
            
            for (i, measurement) in recent.iter().enumerate() {
                let weight = 1.0 / (i + 1) as f64;
                weighted_sum += measurement.bandwidth * weight;
                total_weight += weight;
            }
            
            weighted_sum / total_weight
        }
    }

    /// Add measurement
    pub fn add_measurement(&mut self, measurement: BandwidthMeasurement) {
        if self.measurements.len() >= self.max_history {
            self.measurements.pop_front();
        }
        
        self.current_estimate = measurement.bandwidth;
        self.measurements.push_back(measurement);
    }
}

impl PrefetchPredictor {
    /// Create new prefetch predictor
    pub fn new() -> Self {
        Self {
            access_history: VecDeque::new(),
            prediction_model: PredictionModel {
                threshold: 0.7,
                lookahead: 3,
                confidence: 0.0,
            },
            accuracy: 0.0,
        }
    }

    /// Predict next access
    pub fn predict_next(&self) -> Option<usize> {
        // Simple pattern detection (can be enhanced with ML)
        if self.access_history.len() < 3 {
            return None;
        }

        // Look for repeated access patterns
        // Placeholder implementation
        None
    }

    /// Record access
    pub fn record_access(&mut self, pattern: AccessPattern) {
        if self.access_history.len() >= 1000 {
            self.access_history.pop_front();
        }
        
        self.access_history.push_back(pattern);
        self.update_model();
    }

    /// Update prediction model
    fn update_model(&mut self) {
        // Update model based on history
        // Placeholder implementation
    }
}

impl PinnedMemoryCache {
    /// Create new pinned memory cache
    pub fn new(max_pinned_memory: usize) -> Self {
        Self {
            cache: RwLock::new(HashMap::new()),
            max_pinned_memory,
            current_usage: Arc::new(RwLock::new(0)),
            lru_queue: Mutex::new(VecDeque::new()),
        }
    }

    /// Allocate pinned memory
    pub fn allocate(&self, size: usize) -> RusTorchResult<PinnedAllocation> {
        // Check cache for available allocation
        let mut cache = self.cache.write().unwrap();
        
        for (id, allocation) in cache.iter_mut() {
            if !allocation.in_use && allocation.size >= size {
                allocation.in_use = true;
                allocation.last_used = Instant::now();
                return Ok(allocation.clone());
            }
        }

        // Allocate new pinned memory
        let mut current = self.current_usage.write().unwrap();
        
        if *current + size > self.max_pinned_memory {
            // Evict LRU entries
            self.evict_lru(size)?;
        }

        // Platform-specific pinned allocation
        let host_ptr = self.allocate_pinned_memory(size)?;
        
        let allocation = PinnedAllocation {
            host_ptr,
            size,
            in_use: true,
            last_used: Instant::now(),
        };

        *current += size;
        cache.insert(host_ptr, allocation.clone());

        Ok(allocation)
    }

    /// Platform-specific pinned memory allocation
    fn allocate_pinned_memory(&self, size: usize) -> RusTorchResult<usize> {
        // Platform-specific implementation
        Ok(0) // Placeholder
    }

    /// Evict LRU entries
    fn evict_lru(&self, required_size: usize) -> RusTorchResult<()> {
        // Evict least recently used entries
        // Placeholder implementation
        Ok(())
    }

    /// Release pinned allocation
    pub fn release(&self, host_ptr: usize) -> RusTorchResult<()> {
        let mut cache = self.cache.write().unwrap();
        
        if let Some(allocation) = cache.get_mut(&host_ptr) {
            allocation.in_use = false;
            allocation.last_used = Instant::now();
        }

        Ok(())
    }
}

impl UnifiedMemoryManager {
    /// Create new unified memory manager
    pub fn new() -> Self {
        Self {
            allocations: Arc::new(RwLock::new(HashMap::new())),
            coherence_protocol: CoherenceProtocol::WriteBack,
            migration_policy: MigrationPolicy {
                threshold: 0.7,
                eager_migration: false,
                granularity: MigrationGranularity::Page,
            },
            fault_handler: Arc::new(PageFaultHandler::new()),
        }
    }

    /// Allocate unified memory
    pub fn allocate(&self, size: usize) -> RusTorchResult<UnifiedAllocation> {
        // Platform-specific unified memory allocation
        let virtual_addr = self.allocate_unified_memory(size)?;
        
        let allocation = UnifiedAllocation {
            id: self.generate_allocation_id(),
            virtual_addr,
            size,
            residency: MemoryLocation::Unified,
            access_counters: AccessCounters::default(),
            migration_history: Vec::new(),
        };

        let mut allocations = self.allocations.write().unwrap();
        allocations.insert(allocation.id, allocation.clone());

        Ok(allocation)
    }

    /// Handle page fault
    pub fn handle_fault(&self, addr: usize, is_gpu: bool) -> RusTorchResult<()> {
        self.fault_handler.handle(addr, is_gpu, &self.migration_policy)
    }

    /// Platform-specific unified memory allocation
    fn allocate_unified_memory(&self, size: usize) -> RusTorchResult<usize> {
        // Platform-specific implementation
        Ok(0) // Placeholder
    }

    /// Generate unique allocation ID
    fn generate_allocation_id(&self) -> usize {
        use std::sync::atomic::{AtomicUsize, Ordering};
        static COUNTER: AtomicUsize = AtomicUsize::new(0);
        COUNTER.fetch_add(1, Ordering::SeqCst)
    }
}

impl PageFaultHandler {
    /// Create new page fault handler
    pub fn new() -> Self {
        Self {
            fault_stats: RwLock::new(FaultStatistics::default()),
            resolution_strategy: ResolutionStrategy::Immediate,
        }
    }

    /// Handle page fault
    pub fn handle(&self, addr: usize, is_gpu: bool, policy: &MigrationPolicy) -> RusTorchResult<()> {
        let start = Instant::now();
        
        // Update statistics
        let mut stats = self.fault_stats.write().unwrap();
        stats.total_faults += 1;
        
        if is_gpu {
            stats.gpu_faults += 1;
        } else {
            stats.cpu_faults += 1;
        }

        // Resolve fault based on strategy
        match self.resolution_strategy {
            ResolutionStrategy::Immediate => {
                // Immediate migration
                self.migrate_page(addr, is_gpu, policy)?;
            },
            ResolutionStrategy::Deferred => {
                // Queue for deferred migration
                self.queue_migration(addr, is_gpu)?;
            },
            ResolutionStrategy::Replicated => {
                // Create replica
                self.replicate_page(addr)?;
            },
        }

        // Update average resolution time
        let duration = start.elapsed();
        let total_time = stats.avg_resolution_time.as_secs_f64() * (stats.total_faults - 1) as f64;
        stats.avg_resolution_time = Duration::from_secs_f64(
            (total_time + duration.as_secs_f64()) / stats.total_faults as f64
        );

        Ok(())
    }

    /// Migrate page
    fn migrate_page(&self, addr: usize, to_gpu: bool, policy: &MigrationPolicy) -> RusTorchResult<()> {
        // Platform-specific page migration
        Ok(())
    }

    /// Queue migration for deferred execution
    fn queue_migration(&self, addr: usize, to_gpu: bool) -> RusTorchResult<()> {
        // Queue implementation
        Ok(())
    }

    /// Replicate page for shared access
    fn replicate_page(&self, addr: usize) -> RusTorchResult<()> {
        // Replication implementation
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_gpu_memory_allocator() {
        let pool = Arc::new(MemoryPool::new(Default::default()));
        let allocator = GpuMemoryAllocator::new(0, 1024 * 1024 * 1024, pool);
        
        // Test allocation
        let result = allocator.allocate(1024 * 1024);
        assert!(result.is_ok());
        
        // Test stats
        let stats = allocator.memory_stats();
        assert_eq!(stats.device_id, 0);
        assert!(stats.used_memory > 0);
    }

    #[test]
    fn test_transfer_optimizer() {
        let optimizer = TransferOptimizer::new(TransferConfig::default());
        
        let request = TransferRequest {
            id: 1,
            source: MemoryLocation::Host,
            destination: MemoryLocation::Device(0),
            size: 1024 * 1024,
            priority: TransferPriority::Normal,
            is_async: true,
            callback: None,
        };
        
        let result = optimizer.optimize_and_execute(request);
        assert!(result.is_ok());
    }

    #[test]
    fn test_bandwidth_estimator() {
        let mut estimator = BandwidthEstimator::new();
        
        // Add measurement
        estimator.add_measurement(BandwidthMeasurement {
            direction: TransferDirection::HostToDevice,
            bytes: 1024 * 1024,
            duration: Duration::from_millis(1),
            bandwidth: 1e9,
            timestamp: Instant::now(),
        });
        
        // Test estimation
        let estimate = estimator.estimate(TransferDirection::HostToDevice);
        assert!(estimate > 0.0);
    }

    #[test]
    fn test_pinned_memory_cache() {
        let cache = PinnedMemoryCache::new(1024 * 1024);
        
        // Test allocation
        let result = cache.allocate(1024);
        assert!(result.is_ok());
        
        if let Ok(allocation) = result {
            // Test release
            let release_result = cache.release(allocation.host_ptr);
            assert!(release_result.is_ok());
        }
    }

    #[test]
    fn test_unified_memory_manager() {
        let manager = UnifiedMemoryManager::new();
        
        // Test allocation
        let result = manager.allocate(1024 * 1024);
        assert!(result.is_ok());
    }
}