TCS Placement: Sample Questions 139 - 139 of 502
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Question 139
Explanation
- It is the transfer of sufficient amount of the state of process from one machine to the target machine.
- Process migration is the relocation of a process from its source node to another destination node.
- A process can either be migrated before it starts execution on its source node which is called as non-preemptive process or during the course of its execution that is known as preemptive process migration.
- Preemptive process migration is more costly compared to non-preemptive because the process environment must accompany the process to its new node.
- Steps involved in process migration:
- Process is selected for migration.
- Select destination node for the process to be migrated.
- Transfer of selected process to the destination node.
- Migration policy is responsible for first two steps while third step is handles by migration mechanism.
- Migration of a process is complex that involves handling various activities to meet the requirements for a good process migration.
- The sub activities involved are:
- Freezing the process on its source node and restarting it on destination node
- Transferring the processes address space from restarting from its source to destination node.
- Forwarding messages meant for the migrant process.
- Handling communication between processes that have been placed at different nodes.
- A preemptive process migration facility allows the transfer of an executing process from one node to another.
- On the other hand, in system supporting only non-preemptive migration facility, a process can only be transferred prior to beginning its execution.
- Preemptive process migration is costlier than non-preemptive process migration since the process state, which must accompany the process to its new node, becomes much more complex after execution begins
Advantages of process migration:
- Reducing average response time of processes
To reduce the average response time of the processes, processes of a heavily loaded node are migrated to idle or underutilized nodes.
- Speeding up individual jobs
- A migration of job to different node is done and executes them concurrently.
- Migrate a job to a node having a faster CPU or to a node at which it has minimum turnaround time.
- More speed up more migration cost involved.