Thrashing in Operating System

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                When a program need space larger than RAM or it need space when RAM is full, Operating System will try to allocate space from secondary memory and behaves like it has that much amount of memory by serving to that program. This concept is called virtual memory. To know about thrashing we first need to know what is page fault and swapping.

Page fault and swapping:

                    We know every program divided into some pages. When a program need a page which is not in RAM that is called page fault. Whenever a page fault happens, operating system will try to fetch that page from secondary memory and try to swap it with one of the page in RAM. This is called swapping.

What is Thrashing  in OS?

If this page fault and then swapping happening very frequently at higher rate, then operating system has to spend more time to swap these pages. This state is called thrashing. Because of this, CPU utilization is going to be reduced.

Effect of Thrashing

Whenever thrashing starts, operating system tries to apply either Global page replacement Algorithm or Local page replacement algorithm.

Global Page Replacement

Since global page replacement can access to bring any page, it tries to bring more pages whenever thrashing found. But what actually will happen is, due to this, no process gets enough frames and by result thrashing will be increase more and more. So global page replacement algorithm is not suitable when thrashing happens.

Local Page Replacement

Unlike global page replacement algorithm, local page replacement will select pages which only belongs to that process. So there is a chance to reduce the thrashing. But it is proven that there are many disadvantages if we use local page replacement. So local page replacement is just alternative than global page replacement in thrashing scenario.

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1. What is an Operating System ?
2. Discuss the structure off OS ?
3. Explain type of OS?
4. Explain Function of OS?
5. Explain OS Services ?
6. What do mean by system call ?List different type ofsystem call available ?

1. what is process ? and Characteristics ?
2. What is different process state? explain the same in details?
3. write short note on user level and kernal level threads?
4. explain what is thread and its type ?
5. explain scheduler ? (short term,medium term,and long term)
6. state and explain scheduling criteria ?
7. Explain scheduling algorithm ? [ FCFS,SJF,PRIORITY,ROUND ROBINE.]    

1. What is process synchronization ? explain critical section problem and race condition ?
2. what is Race Condition ?
3. what is critical section problem?
4. explain classical problem of synchronization?
5. explain bounded - buffer problem?
6. explain reader - writer problem ?
7. explain Dining Philosophers Problem ?
8. explain semaphores ? its type ?

1.  What is deadlock ?
2. What are the 4 condition to produce deadlock ?
3. explain methods of handling deadlock ?
4. explain in detail deadlock prevention ?
5. write short note on deadlock avoidance ?
6. explain deadlock detection ? 
7. explain Banker algorithm with example ? 

1. What are memory management ?
2. what is contiguous memory allocation and non - contiguous memory allocation ?
3. explain concept of paging with neat diagram?
4. differentiate contiguous and non - contiguous memory allocation ?
5. explain in details various partitioning memory management?
6. explain the concept of Segmentation ?
7. what is Thrashing explain in details ?

1. explain virtual memory concept in details ? with advantages and disadvantages ?
2. explain page replacement algorithm ?
3. explain LRU , Optimal ,FIFO.