Skip to main content

Thrashing in Operating System (OS)

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.

Thrashing in Operating System (OS)

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.

Techniques to Handle Thrashing

We already seen Local replacement is better than Global replacement to avoid thrashing. But it also has disadvantages and not suggestable. Some more techniques are

Working Set Model

This model is based on locality. What locality is saying, the page used recently can be used again and also the pages which are nearby this page will also be used. Working set means set of pages in the most recent D time. The page which completed its D amount of time in working set automatically dropped from it. So accuracy of working set depends on D we have chosen. This working set model avoid thrashing while keeping the degree of multiprogramming as high as possible.

Page Fault Frequency

Page Fault Frequency

It is some direct approach than working set model. When thrashing occurring we know that it has few number of frames. And if it is not thrashing that means it has too many frames. Based on this property we assign an upper and lower bound for the desired page fault rate. According to page fault rate we allocate or remove pages. If the page fault rate become less than the lower limit, frames can be removed from the process. Similarly, if the page fault rate become more than the upper limit, more number of frames can be allocated to the process. And if no frames available due to high page fault rate, we will just suspend the processes and will restart them again when frames available.

Source: https://www.geeksforgeeks.org/operating-system-techniques-handle-thrashing/

The post Thrashing in Operating System (OS) appeared first on The Crazy Programmer.



from The Crazy Programmer https://www.thecrazyprogrammer.com/2019/02/thrashing-in-operating-system-os.html
Labels:

Comments

Post a Comment

Popular posts from this blog

Rail Fence Cipher Program in C and C++[Encryption & Decryption]

Here you will get rail fence cipher program in C and C++ for encryption and decryption. It is a kind of transposition cipher which is also known as zigzag cipher. Below is an example. Here Key = 3. For encryption we write the message diagonally in zigzag form in a matrix having total rows = key and total columns = message length. Then read the matrix row wise horizontally to get encrypted message. Rail Fence Cipher Program in C #include<stdio.h> #include<string.h> void encryptMsg(char msg[], int key){ int msgLen = strlen(msg), i, j, k = -1, row = 0, col = 0; char railMatrix[key][msgLen]; for(i = 0; i < key; ++i) for(j = 0; j < msgLen; ++j) railMatrix[i][j] = '\n'; for(i = 0; i < msgLen; ++i){ railMatrix[row][col++] = msg[i]; if(row == 0 || row == key-1) k= k * (-1); row = row + k; } printf("\nEncrypted Message: "); for(i = 0; i < key; ++i) f...
3 comments
Read more

Data Encryption Standard (DES) Algorithm

Data Encryption Standard is a symmetric-key algorithm for the encrypting the data. It comes under block cipher algorithm which follows Feistel structure. Here is the block diagram of Data Encryption Standard. Fig1: DES Algorithm Block Diagram [Image Source: Cryptography and Network Security Principles and Practices 4 th Ed by William Stallings] Explanation for above diagram: Each character of plain text converted into binary format. Every time we take 64 bits from that and give as input to DES algorithm, then it processed through 16 rounds and then converted to cipher text. Initial Permutation: 64 bit plain text goes under initial permutation and then given to round 1. Since initial permutation step receiving 64 bits, it contains an 1×64 matrix which contains numbers from 1 to 64 but in shuffled order. After that, we arrange our original 64 bit text in the order mentioned in that matrix. [You can see the matrix in below code] After initial permutation, 64 bit text passed throug...
Post a Comment
Read more

dotnet sdk list and dotnet sdk latest

Can someone make .NET Core better with a simple global command? Fanie Reynders did and he did it in a simple and elegant way. I'm envious, in fact, because I spec'ed this exact thing out in a meeting a few months ago but I could have just done it like he did and I would have used fewer keystrokes! Last year when .NET Core was just getting started, there was a "DNVM" helper command that you could use to simplify dealing with multiple versions of the .NET SDK on one machine. Later, rather than 'switching global SDK versions,' switching was simplified to be handled on a folder by folder basis. That meant that if you had a project in a folder with no global.json that pinned the SDK version, your project would use the latest installed version. If you liked, you could create a global.json file and pin your project's folder to a specific version. Great, but I would constantly have to google to remember the format for the global.json file, and I'd constan...
Post a Comment
Read more