Ageing

🧠 What is Aging (or Ageing)?

Aging is a technique used in CPU scheduling to gradually increase the priority of waiting processes so that they eventually get the CPU and don’t starve.

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🎯 Why Aging?

When a process has been waiting in the ready queue for too long, the system:

• Boosts its priority periodically

• This ensures that it doesn’t wait forever, even in a priority-based scheduling system

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🧩 Example (Priority Scheduling without Aging)

Time	Process	Priority (Lower is better)
0	P1	1
1	P2	1
2	P3	1
3	P4	5 ← Low priority

• P4 may never run because new high-priority processes keep arriving

• This is starvation

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✅ With Aging

• Every 5 seconds, increase P4’s priority by 1 step

• Eventually:
  P4 priority: 5 → 4 → 3 → 2 → 1

• Now it competes fairly and gets CPU

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⚙️ How It’s Implemented (Simple Pseudocode)

for process in ready_queue:
    if process.wait_time > aging_threshold:
        process.priority -= 1  # higher priority

• aging_threshold can be tuned (e.g., 10 seconds)

• The lower the priority value, the sooner it gets CPU

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🧠 Key Points

Property	Value
📦 Type	Dynamic priority adjustment
✅ Prevents	Starvation in priority-based and SJF algorithms
🧠 Common In	Multilevel Feedback Queues, Linux CFS
🧪 Tradeoff	Slightly more complex scheduler, but fairer

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🧠 Interview-Ready Definition:

Aging is a technique used to prevent starvation by gradually increasing the priority of waiting processes in the ready queue. This ensures that even low-priority or long-duration jobs eventually get scheduled for CPU execution.

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🧠 One-Liner for Interviews:

“Aging prevents starvation by slowly boosting a waiting process’s priority until it gets its fair turn.”

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🖥️ Real-World Analogy

You’re at the end of a queue at a food stall.
Every 5 minutes, you’re allowed to move one position forward — even if VIPs keep arriving.
Eventually, you get your food — that’s aging.