20.4.3. Proportional Allocation Scheme

Now, allocation of frames; now still now we are saying that a page does not a page frames have no connection with the processes. Now, this is entirely not true. So, each process requires a minimum number of frames. So, typically what do we do is that we allocate a certain number of physical page frames to each process. However, this is done using many schemes, there can be a fixed allocation scheme, there can be there can be a prioritized allocation scheme and it has many variations.

This chunk introduces the concept of frame allocation schemes. It explains that every process running in a system needs a certain number of frames (or memory pages) to operate efficiently. Without sufficient frames, processes may face inefficiencies, such as increased page faults. Frame allocation can be approached in several ways, including fixed allocation, proportional allocation, and priority-based allocation schemes.

Imagine a library where different types of books are stored. Each section (like fiction, textbooks, or magazines) needs a certain number of shelves (frames) to display its books. If one section doesn't have enough shelves, it might face overcrowding and chaos, making it hard for readers to find what they're looking for. Similarly, processes in a computer need adequate frames to function smoothly.

For example, the first strategy is to is the fixed allocation scheme. In the fixed allocation scheme let us say I have 100 frames in physical memory after these 100 frames are available after allocating frames to the OS and I have 5 processes. So, the degree of multi programming is 5, I give each process 20 frames, I divide the frames into this into this 5 processes. So, this one will be called a fixed allocation, fixed allocation.

The fixed allocation scheme is a simplistic approach where a certain number of frames are predetermined and assigned to each process. In this example, 100 frames are available, and with 5 processes running, each process is allocated 20 frames regardless of its specific needs. This method is straightforward but can lead to inefficiencies if a process doesn't require all its allocated frames.

Consider a restaurant that has fixed seating arrangements. If a large group comes in but only needs one table for their meeting, other available tables go unused, limiting the restaurant's ability to serve more patrons. This is akin to fixed allocation, which might leave some memory spaces underutilized.

Otherwise we can do a proportional allocation, I allocate fairly based on the process size. So, for example, let us say let 𝑠 be the size of process 𝑃 and 𝑆 be the total summation of the pages over all processes that are currently active. And let 𝑚 be the total number of frames that are there in physical memory. So, then the number of frames that will be allocated to a certain process to process 𝑃; 𝑎 that will be allocated to process the process 𝑖 will be given by 𝑖 × 𝑚 / 𝑆.

Proportional allocation is a more flexible approach. Instead of giving each process the same number of frames, the number of frames is distributed based on the size of each process relative to all active processes. This method allows larger processes to receive more frames, which can improve overall memory efficiency and application performance.

Think of sharing a pizza among friends based on their hunger levels. If one friend is really hungry, they get a larger slice of pizza, while others who are less hungry get smaller slices. This way, everyone is satisfied according to their needs, similar to how proportional allocation adapts to the memory needs of processes.

Now, priority based allocation is proportional allocation using priorities. Now, instead of sizes, I use priorities. So, if process 𝑃 generates a page fault select for replacement 1 of its frames is available, otherwise select for replacement of a frame from a process with lower priority number.

Priority-based allocation builds on proportional allocation by introducing priority levels for processes. Processes with higher priority levels can access frames before those with lower priority. This allocation method ensures that critical processes maintain higher performance, particularly during intense workloads when memory is constrained.

Imagine a hospital emergency room where patients are treated based on the severity of their condition. A patient with a life-threatening injury (higher priority) gets immediate access to a doctor, while others with less urgent needs (lower priority) wait. Priority-based allocation maintains system efficiency by ensuring that the most vital processes receive the resources they need promptly.

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