Resource Allocation - aryanjoshi0823/5143-Operating-System GitHub Wiki

Resource Allocation in Operating Systems

Resource allocation is a core function of an operating system (OS). It involves managing and distributing hardware and software resources such as CPU, memory, I/O devices, and storage to various processes effectively. The goal is to optimize resource usage while ensuring fairness, efficiency, and system stability.

Resource Allocation Strategies

1. Static Allocation: Resources are allocated at compile time or process creation.

2. Dynamic Allocation Resources are allocated during process execution.

3. Preemptive Allocation

  • Resources can be forcibly reclaimed by the OS for allocation to another process.
  • Time-sharing systems.
  • CPU preemption using a round-robin scheduler.

4. Non-Preemptive Allocation

  • Once allocated, resources cannot be reclaimed until the process releases them.
  • I/O operations and critical sections.

Resource Allocation Techniques

1. Resource Scheduling

  • CPU Scheduling:
    • Algorithms include First-Come-First-Serve (FCFS), Shortest Job Next (SJN), Round Robin (RR), and Priority Scheduling.
    • Ensures fairness and efficiency in CPU usage.
  • I/O Scheduling:
    • Algorithms like Shortest Seek Time First (SSTF) and Elevator Algorithm manage disk I/O requests.
  • Memory Scheduling:
    • Virtual memory techniques allocate memory pages dynamically.

2. Resource Partitioning

  • Divides resources into fixed or variable partitions.
  • Example:
    • Disk partitions.
    • Fixed-size memory blocks.

3. Resource Allocation Graphs (RAG)

  • A graph-based method to detect and avoid deadlocks.
    • Nodes: Represent processes and resources.
    • Edges:
      • Request edge (P → R): Process requests a resource.
      • Assignment edge (R → P): Resource is allocated to a process.

4. Priority-Based Allocation

  • Processes are assigned priorities, and resources are allocated based on these priorities.
  • Can lead to priority inversion, where low-priority processes block high-priority ones.

5. Banker's Algorithm

  • Purpose: Avoid deadlocks.
  • Process:
    1. Check if a resource request can be safely granted without entering a deadlock state.
    2. Allocate resources only if the system remains in a safe state.