TLB and Page Table Simulation

Virtual memory management system implementation

TLB and Page Table Simulation

Overview

A comprehensive virtual memory simulation project implementing Translation Lookaside Buffer (TLB) and its interfacing with Page Tables, developed as part of the Computer Architecture course.

Project Details

Duration: October 2023
Course: ECN-207 (Computer Architecture)
Implementation: C++
Role: Course Project

Objectives

  • Implement a working model of virtual memory management
  • Simulate TLB operations and caching behavior
  • Demonstrate address translation mechanisms
  • Analyze performance trade-offs in memory hierarchies

System Architecture

Components Implemented

  1. Translation Lookaside Buffer (TLB)
    • Associative cache for page table entries
    • Configurable size and associativity
    • Replacement policy implementation (LRU, FIFO)
    • Hit/miss statistics tracking
  2. Page Table
    • Multi-level page table structure
    • Virtual to physical address mapping
    • Page fault handling
    • Access permission management
  3. Memory Management Unit (MMU)
    • Address translation logic
    • TLB lookup mechanism
    • Page table walk implementation
    • Exception handling

Technical Implementation

Address Translation Process

Virtual Address → TLB Lookup → Hit? Yes → Physical Address
                            ↓ No
                     Page Table Walk → Physical Address
                                    ↓
                              Update TLB

Key Features

  • TLB Management
    • Fast associative lookup
    • Multiple replacement policies
    • Entry invalidation on context switch
    • Performance monitoring
  • Page Table Structure
    • Two-level hierarchical design
    • Page directory and page tables
    • 4KB page size (configurable)
    • Present/absent bit handling
  • Address Space
    • 32-bit virtual addressing
    • Configurable physical memory size
    • Support for demand paging
    • Shared page support

Simulation Scenarios

Test Cases Implemented

  1. Sequential Access Pattern
    • Memory access patterns with spatial locality
    • TLB performance with sequential reads
    • Page table walk frequency analysis
  2. Random Access Pattern
    • Worst-case TLB performance
    • High page fault rates
    • Replacement policy effectiveness
  3. Working Set Simulation
    • Realistic application behavior
    • Temporal locality effects
    • TLB sizing impact
  4. Context Switching
    • TLB flush operations
    • Performance degradation analysis
    • Multi-process simulation

Performance Metrics

Measured Parameters

  • TLB Hit Rate: Percentage of addresses resolved in TLB
  • Page Fault Rate: Frequency of page table misses
  • Average Access Time: Combined TLB and page table latency
  • Translation Overhead: Cost of address translation

Results

  • TLB hit rates: 85-98% for typical workloads
  • Significant performance improvement over page table only
  • Replacement policy impact on performance
  • Optimal TLB size determination

Implementation Details

C++ Design

class TLB {
    - Entry structure (VPN, PPN, Valid, Dirty)
    - lookup(virtual_addr)
    - insert(vpn, ppn)
    - evict() with replacement policy
}

class PageTable {
    - Multi-level structure
    - walk(virtual_addr)
    - allocate_page()
    - handle_page_fault()
}

class MMU {
    - translate_address()
    - handle_tlb_miss()
    - update_statistics()
}

Data Structures

  • Hash tables for fast TLB lookup
  • Tree structures for page table hierarchy
  • Linked lists for LRU implementation
  • Bit vectors for tracking valid entries

Configuration Options

  • TLB size: 16, 32, 64, 128 entries
  • Associativity: Direct-mapped, 2-way, 4-way, fully associative
  • Page size: 4KB, 8KB, 16KB
  • Replacement policies: LRU, FIFO, Random
  • Address space size: configurable

Key Learnings

Virtual Memory Concepts

  • Importance of TLB in system performance
  • Trade-offs between TLB size and hit rate
  • Impact of locality on translation performance
  • Multi-level page tables for large address spaces

Computer Architecture

  • Memory hierarchy design principles
  • Caching strategies and policies
  • Hardware-software interface
  • Performance optimization techniques

Extensions and Enhancements

  • Multi-core TLB coherence simulation
  • Large page support (2MB, 1GB pages)
  • ASID (Address Space ID) for context switching
  • TLB prefetching mechanisms

Applications

This simulation helps understand:

  • Operating system memory management
  • Virtual machine implementations
  • Processor design considerations
  • Performance tuning for memory-intensive applications

This project provided deep insights into one of the most critical components of modern computer systems, bridging the gap between virtual and physical memory.