Thrashing in Operating System

Thrashing in operating system is a condition where the system keeps switching data between the RAM and the hard disk too often, leaving little time for actual processing. This usually happens when there are too many programs running and not enough memory to handle them all. This affects the performance of the computer, and even simple tasks take a long time to respond. In this blog, you will learn what thrashing in operating system is, how it happens, how to recognize it, and the best ways to prevent it in detail with examples.

Table of Contents:

• What is Thrashing in Operating System
• Symptoms of Thrashing in Operating System
• Causes of Thrashing in Operating System
• Locality of Reference and Working Set in Thrashing
• Techniques to Prevent Thrashing in Operating System
• Algorithms Used During Thrashing in Operating System
• Difference Between Thrashing and Swapping in Operating System
• Real-World Examples of Thrashing in Operating System
• Conclusion

What is Thrashing in Operating System

Thrashing in an operating system is a process in which a computer spends most of its time moving data between the RAM, which is the main memory, and the hard disk. This constant swapping of data is called paging, and when this swapping becomes excessive, it is called thrashing. Thrashing is when a system cannot run properly because it is too busy trying to manage memory pages. This results in the system slowing down significantly and experiencing a major drop in performance.

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Symptoms of Thrashing in Operating System

Let’s explore some of the symptoms of thrashing in operating system:

1. High CPU Usage: The CPU remains highly active but performs very little useful work. Most of its time is spent handling page faults instead of running actual programs.
2. Heavy Disk I/O Activity: You may notice the hard disk constantly working. This is because the system keeps swapping pages in and out of memory, increasing disk input/output operations.
3. Frequent Page Faults: Thrashing in operating system leads to continuous page faults—when the system tries to access data that isn’t in RAM. If this keeps happening, performance drops further.
4. Slow System and App Response: Applications may take longer to open, freeze, or crash. This slowdown happens because the system is too busy swapping memory pages to perform real tasks.

Causes of Thrashing in Operating System

Let’s explore the major causes of thrashing in operating systems:

1. Excessive Multiprogramming: When too many processes run at once, memory demand increases. This overload can trigger thrashing as memory struggles to support all active processes.
2. Poor Memory Management Policy: If the operating system allocates memory inefficiently or fails to manage virtual memory properly, it leads to more page faults and causes thrashing.
3. Lack of Physical Memory: When RAM is insufficient, the system constantly swaps data in and out of memory, increasing disk I/O and leading to thrashing.
4. Poor Page Replacement Policies: When inefficient algorithms remove important pages, the system faces frequent page faults and excessive swapping, which results in thrashing.

Locality of Reference and Working Set in Thrashing

To understand how thrashing occurs and how to prevent it, we need to discuss the Locality Model. The model is based on the observation that programs do not access memory randomly, but rather access memory in a specific and predictable manner. This is referred to as the locality of reference.

1. Locality of Reference

Locality of reference states that programs tend to repeatedly access a small amount of memory for a short period of time. There are three types of locality:

• Temporal Locality: If a program accesses a memory location, it is likely to access that again.
• Spatial Locality: If a program accesses one memory location, it is likely to access a memory location that is physically adjacent to the first one.
• Sequential Locality: Instructions and data usually have sequential access.

2. Role of the Working Set in Preventing Thrashing

The working set is the set of memory pages a program requires during a certain time interval of execution. As long as all of these pages are in memory, the execution of the program is problem-free. 

Ways to avoid thrashing:

• The system must ensure that the working set of each program fits within the available physical memory.
• If there is not enough memory to hold the working sets of all running programs, the operating system should reduce the number of active programs to avoid thrashing.
• The working set model helps the operating system decide which pages should stay in memory and which can be swapped out, ensuring efficient memory usage and reducing the chances of thrashing.

Techniques to Prevent Thrashing in Operating System

Let’s explore some techniques that help to prevent thrashing:

1. Adjust the Degree of Multiprogramming: Reduce the number of active processes running at once. This frees up memory and ensures smoother execution of current tasks.
2. Use the Working Set Model: Track recently used pages of each process. If memory demand is too high, suspend some processes to avoid thrashing.
3. Apply Local Page Replacement: Allow processes to replace only their own pages. This improves stability by isolating memory faults within individual processes.
4. Implement Load Control: Limit how many processes are running concurrently. During thrashing, stop or delay some processes to ease memory pressure.
5. Increase Physical Memory or Optimize Swapping: Add more RAM or ensure fast and efficient swap space usage. This helps reduce the frequency and impact of page faults.

Algorithms Used During Thrashing in Operating System

Some memory management algorithms have better memory management features and are better suited for dealing with thrashing. Examples include:

1. Least Recently Used (LRU): Replaces the page that has not been used for the longest period, assuming that any pages that have been used recently are more likely to be used again.
2. Working Set Algorithm: Tracks the working set of each process, or the active pages of each process, meaning that the algorithm will keep only those active pages in memory.
3. Page Fault Frequency (PFF): Monitors how often page faults are occurring. If the fault rate is too high, the system may reduce the number of processes.
4. FIFO (First In First Out): Pages are replaced when the oldest page in memory is chosen. FIFO is simple, but not always effective. It can also contribute to thrashing if not used responsibly.

Difference Between Thrashing and Swapping in Operating System

Real-World Examples of Thrashing in Operating System

Let’s explore some real-life situations where thrashing can take place:

1. Running Virtual Machines on Low-RAM Systems: Running a virtual machine on limited RAM leads to frequent memory swapping, as both host and guest OS compete for memory. This results in thrashing and system slowdown.
2. Opening Too Many Browser Tabs or Applications: Launching multiple Chrome tabs and heavy apps at once exhausts memory quickly. The OS starts paging constantly, leading to poor performance.
3. Running Heavy Applications on Low-End Devices: Using tools like Photoshop or Android Studio on low-RAM systems forces constant swapping. This slows down the system due to excessive disk usage.
4. Background Services and Antivirus Scans: Antivirus scans running along with the system updates consume high memory. This leads to repeated page faults and causes thrashing.

Conclusion

Thrashing is a critical issue in operating systems where the system constantly swaps data between RAM and disk, leaving very little time for actual program execution. This leads to reduced performance and efficiency. The main causes include excessive memory usage, too many concurrent programs, and poor memory management. It can severely affect responsiveness and interrupt the productive tasks. Preventing thrashing requires careful memory allocation, efficient scheduling, and keeping the active workload within system limits.

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