Program for Best Fit algorithm in Memory Management using Linked List
Last Updated :
23 Feb, 2023
Best fit algorithm for memory management: The memory partition in which there is a minimum loss on the allocation of the process is the best-fit memory partition that is allocated to the process.
We have already discussed one best-fit algorithm using arrays in this article. However, here we are going to look into another approach using a linked list where the deletion of allocated nodes is also possible.
Examples:
Input : blockSize[] = {100, 500, 200}
processSize[] = {95, 417, 112, 426}
Output :
Block with size 426 can't be allocated
Tag Block ID Size
0 0 95
1 1 417
2 2 112
After deleting node with tag id 1.
Tag Block ID Size
0 0 95
2 2 112
3 1 426
Approach: The idea is to assign a unique tag id to each memory block. Each process of different sizes are given block id, which signifies to which memory block they belong to, and unique tag id to delete particular process to free up space. Create a free list of given memory block sizes and allocated list of processes.
Create allocated list:
Create an allocated list of given process sizes by finding the most appropriate or best memory block to allocate memory from. If the memory block is not found, then simply print it. Otherwise, create a node and add it to the allocated linked list.
Delete process:
Each process is given a unique tag id. Delete the process node from the allocated linked list to free up some space for other processes. After deleting, use the block id of the deleted node to increase the memory block size in the free list.
Below is the implementation of the approach:
C++
// C++ implementation of program
// for best fit algorithm for memory
// management using linked list
#include <bits/stdc++.h>
using namespace std;
// Two global counters
int g = 0, k = 0;
// Structure for free list
struct free {
int tag;
int size;
struct free* next;
}* free_head = NULL, *prev_free = NULL;
// Structure for allocated list
struct alloc {
int block_id;
int tag;
int size;
struct alloc* next;
}* alloc_head = NULL, *prev_alloc = NULL;
// Function to create free
// list with given sizes
void create_free(int c)
{
struct free* p = (struct free*)
malloc(sizeof(struct free));
p->size = c;
p->tag = g;
p->next = NULL;
if (free_head == NULL)
free_head = p;
else
prev_free->next = p;
prev_free = p;
g++;
}
// Function to print free list which
// prints free blocks of given sizes
void print_free()
{
struct free* p = free_head;
cout << "Tag\tSize\n";
while (p != NULL) {
cout << p->tag << "\t"
<< p->size << "\n";
p = p->next;
}
}
// Function to print allocated list which
// prints allocated blocks and their block ids
void print_alloc()
{
struct alloc* p = alloc_head;
cout << "Tag\tBlock ID\tSize\n";
while (p != NULL) {
cout << p->tag << "\t " << p->block_id
<< "\t\t" << p->size << "\n";
p = p->next;
}
}
// Function to allocate memory to
// blocks as per Best fit algorithm
void create_alloc(int c)
{
// create node for process of given size
struct alloc* q = (struct alloc*)
malloc(sizeof(struct alloc));
q->size = c;
q->tag = k;
q->next = NULL;
struct free* p = free_head;
// Temporary node r of free
// type to find the best and
// most suitable free node to
// allocate space
struct free* r = (struct free*)
malloc(sizeof(struct free));
r->size = 99999;
// Loop to find best choice
while (p != NULL) {
if (q->size <= p->size) {
if (p->size < r->size)
r = p;
}
p = p->next;
}
// Node found to allocate
// space from
if (r->size != 99999) {
// Adding node to allocated list
q->block_id = r->tag;
r->size -= q->size;
if (alloc_head == NULL)
alloc_head = q;
else {
prev_alloc = alloc_head;
while (prev_alloc->next != NULL)
prev_alloc = prev_alloc->next;
prev_alloc->next = q;
}
k++;
}
// Node with size not found
else
cout << "Block with size "
<< c << " can't be allocated\n";
}
// Function to delete node from
// allocated list to free some space
void delete_alloc(int t)
{
// Standard delete function
// of a linked list node
struct alloc *p = alloc_head, *q = NULL;
// First, find the node according
while (p != NULL)
// to given tag id
{
if (p->tag == t)
break;
q = p;
p = p->next;
}
if (p == NULL)
cout << "Tag ID doesn't exist\n";
else if (p == alloc_head)
alloc_head = alloc_head->next;
else
q->next = p->next;
struct free* temp = free_head;
while (temp != NULL) {
if (temp->tag == p->block_id) {
temp->size += p->size;
break;
}
temp = temp->next;
}
}
// Driver Code
int main()
{
int blockSize[] = { 100, 500, 200 };
int processSize[] = { 95, 417, 112, 426 };
int m = sizeof(blockSize)
/ sizeof(blockSize[0]);
int n = sizeof(processSize)
/ sizeof(processSize[0]);
for (int i = 0; i < m; i++)
create_free(blockSize[i]);
for (int i = 0; i < n; i++)
create_alloc(processSize[i]);
print_alloc();
// block of tag id 1 deleted
// to free space for block of size 426
delete_alloc(1);
create_alloc(426);
cout << "After deleting block"
<< " with tag id 1.\n";
print_alloc();
}
# Python3 implementation of the First
# sit memory management algorithm
# using linked list
# Two global counters
g = 0; k = 0
# Structure for free list
class free:
def __init__(self):
self.tag=-1
self.size=0
self.next=None
free_head = None; prev_free = None
# Structure for allocated list
class alloc:
def __init__(self):
self.block_id=-1
self.tag=-1
self.size=0
self.next=None
alloc_head = None;prev_alloc = None
# Function to create free
# list with given sizes
def create_free(c):
global g,prev_free,free_head
p = free()
p.size = c
p.tag = g
p.next = None
if free_head is None:
free_head = p
else:
prev_free.next = p
prev_free = p
g+=1
# Function to print free list which
# prints free blocks of given sizes
def print_free():
p = free_head
print("Tag\tSize")
while (p != None) :
print("{}\t{}".format(p.tag,p.size))
p = p.next
# Function to print allocated list which
# prints allocated blocks and their block ids
def print_alloc():
p = alloc_head
print("Tag\tBlock ID\tSize")
while (p is not None) :
print("{}\t{}\t{}\t".format(p.tag,p.block_id,p.size))
p = p.next
# Function to allocate memory to
# blocks as per First fit algorithm
def create_alloc(c):
global k,alloc_head
# create node for process of given size
q = alloc()
q.size = c
q.tag = k
q.next = None
p = free_head
# Iterate to find first memory
# block with appropriate size
while (p != None) :
if (q.size <= p.size):
break
p = p.next
# Node found to allocate
if (p != None) :
# Adding node to allocated list
q.block_id = p.tag
p.size -= q.size
if (alloc_head == None):
alloc_head = q
else :
prev_alloc = alloc_head
while (prev_alloc.next != None):
prev_alloc = prev_alloc.next
prev_alloc.next = q
k+=1
else: # Node found to allocate space from
print("Block of size {} can't be allocated".format(c))
# Function to delete node from
# allocated list to free some space
def delete_alloc(t):
global alloc_head
# Standard delete function
# of a linked list node
p = alloc_head; q = None
# First, find the node according
# to given tag id
while (p != None) :
if (p.tag == t):
break
q = p
p = p.next
if (p == None):
print("Tag ID doesn't exist")
elif (p == alloc_head):
alloc_head = alloc_head.next
else:
q.next = p.next
temp = free_head
while (temp != None) :
if (temp.tag == p.block_id) :
temp.size += p.size
break
temp = temp.next
# Driver Code
if __name__ == '__main__':
blockSize = [100, 500, 200]
processSize = [417, 112, 426, 95]
m = len(blockSize)
n = len(processSize)
for i in range(m):
create_free(blockSize[i])
for i in range(n):
create_alloc(processSize[i])
print_alloc()
# Block of tag id 0 deleted
# to free space for block of size 426
delete_alloc(0)
create_alloc(426)
print("After deleting block with tag id 0.")
print_alloc()
// Java implementation of program
// for best fit algorithm for memory
// management using linked list
import java.util.*;
// Class for free list
class Free {
int tag;
int size;
Free next;
public Free(int tag, int size)
{
this.tag = tag;
this.size = size;
next = null;
}
}
// Class for allocated list
class Alloc {
int block_id;
int tag;
int size;
Alloc next;
public Alloc(int tag, int size)
{
this.tag = tag;
this.size = size;
next = null;
}
}
public class MemoryManagement {
// Two global counters
static int g = 0, k = 0;
// Head of free list
static Free free_head = null;
static Free prev_free = null;
// Head of allocated list
static Alloc alloc_head = null;
static Alloc prev_alloc = null;
// Function to create free
// list with given sizes
public static void create_free(int c)
{
Free p = new Free(g, c);
if (free_head == null)
free_head = p;
else
prev_free.next = p;
prev_free = p;
g++;
}
// Function to print free list which
// prints free blocks of given sizes
public static void print_free()
{
Free p = free_head;
System.out.println("Tag\tSize");
while (p != null) {
System.out.println(p.tag + "\t" + p.size);
p = p.next;
}
}
// Function to print allocated list which
// prints allocated blocks and their block ids
public static void print_alloc()
{
Alloc p = alloc_head;
System.out.println("Tag\tBlock ID\tSize");
while (p != null) {
System.out.println(p.tag + "\t " + p.block_id
+ "\t\t" + p.size);
p = p.next;
}
}
// Function to allocate memory to
// blocks as per Best fit algorithm
public static void create_alloc(int c)
{
// create node for process of given size
Alloc q = new Alloc(k, c);
Free p = free_head;
// Temporary node r of free
// type to find the best and
// most suitable free node to
// allocate space
Free r = new Free(0, 99999);
// Loop to find best choice
while (p != null) {
if (q.size <= p.size) {
if (p.size < r.size)
r = p;
}
p = p.next;
}
// Node found to allocate
// space from
if (r.size != 99999) {
// Adding node to allocated list
q.block_id = r.tag;
r.size -= q.size;
if (alloc_head == null)
alloc_head = q;
else {
prev_alloc = alloc_head;
while (prev_alloc.next != null)
prev_alloc = prev_alloc.next;
prev_alloc.next = q;
}
k++;
}
// Node with size not found
else
System.out.println("Block with size "
+ c + " can't be allocated\n");
}
// Function to delete node from
// allocated list to free some space
public static void delete_alloc(int t)
{
// Standard delete function
// of a linked list node
Alloc p = alloc_head, q = null;
// First, find the node according
while (p != null)
// to given tag id
{
if (p.tag == t)
break;
q = p;
p = p.next;
}
if (p == null)
System.out.println("Tag ID doesn't exist\n");
else if (p == alloc_head)
alloc_head = alloc_head.next;
else
q.next = p.next;
Free temp = free_head;
while (temp != null) {
if (temp.tag == p.block_id) {
temp.size += p.size;
break;
}
temp = temp.next;
}
}
// Driver Code
public static void main(String[] args)
{
int[] blockSize = new int[] { 100, 500, 200 };
int[] processSize = new int[] { 95, 417, 112, 426 };
int m = blockSize.length;
int n = processSize.length;
for (int i = 0; i < m; i++)
create_free(blockSize[i]);
for (int i = 0; i < n; i++)
create_alloc(processSize[i]);
print_alloc();
// block of tag id 1 deleted
// to free space for block of size 426
delete_alloc(1);
create_alloc(426);
System.out.println("After deleting block"
+ " with tag id 1.");
print_alloc();
}
}
// C# implementation of program
// for best fit algorithm for memory
// management using linked list
using System;
// Class for free list
class Free
{
public int tag;
public int size;
public Free next;
public Free(int tag, int size)
{
this.tag = tag;
this.size = size;
next = null;
}
}
// Class for allocated list
class Alloc
{
public int block_id;
public int tag;
public int size;
public Alloc next;
public Alloc(int tag, int size)
{
this.tag = tag;
this.size = size;
next = null;
}
}
public class MemoryManagement
{
// Two global counters
static int g = 0, k = 0;
// Head of free list
static Free free_head = null;
static Free prev_free = null;
// Head of allocated list
static Alloc alloc_head = null;
static Alloc prev_alloc = null;
// Function to create free
// list with given sizes
public static void create_free(int c)
{
Free p = new Free(g, c);
if (free_head == null)
free_head = p;
else
prev_free.next = p;
prev_free = p;
g++;
}
// Function to print free list which
// prints free blocks of given sizes
public static void print_free()
{
Free p = free_head;
Console.WriteLine("Tag\tSize");
while (p != null)
{
Console.WriteLine(p.tag + "\t" + p.size);
p = p.next;
}
}
// Function to print allocated list which
// prints allocated blocks and their block ids
public static void print_alloc()
{
Alloc p = alloc_head;
Console.WriteLine("Tag\tBlock ID\tSize");
while (p != null)
{
Console.WriteLine(p.tag + "\t " + p.block_id
+ "\t\t" + p.size);
p = p.next;
}
}
// Function to allocate memory to
// blocks as per Best fit algorithm
public static void create_alloc(int c)
{
// create node for process of given size
Alloc q = new Alloc(k, c);
Free p = free_head;
// Temporary node r of free
// type to find the best and
// most suitable free node to
// allocate space
Free r = new Free(0, 99999);
// Loop to find best choice
while (p != null)
{
if (q.size <= p.size)
{
if (p.size < r.size)
r = p;
}
p = p.next;
}
// Node found to allocate
// space from
if (r.size != 99999)
{
// Adding node to allocated list
q.block_id = r.tag;
r.size -= q.size;
if (alloc_head == null)
alloc_head = q;
else
{
prev_alloc = alloc_head;
while (prev_alloc.next != null)
prev_alloc = prev_alloc.next;
prev_alloc.next = q;
}
k++;
}
// Node with size not found
else
Console.WriteLine("Block with size "
+ c + " can't be allocated\n");
}
// Function to delete node from
// allocated list to free some space
public static void delete_alloc(int t)
{
// Standard delete function
// of a linked list node
Alloc p = alloc_head, q = null;
// First, find the node according
while (p != null)
// to given tag id
{
if (p.tag == t)
break;
q = p;
p = p.next;
}
if (p == null)
Console.WriteLine("Tag ID doesn't exist\n");
else if (p == alloc_head)
alloc_head = alloc_head.next;
else
q.next = p.next;
Free temp = free_head;
while (temp != null)
{
if (temp.tag == p.block_id)
{
temp.size += p.size;
break;
}
temp = temp.next;
}
}
// Driver Code
public static void Main(string[] args)
{
int[] blockSize = new int[] { 100, 500, 200 };
int[] processSize = new int[] { 95, 417, 112, 426 };
int m = blockSize.Length;
int n = processSize.Length;
for (int i = 0; i < m; i++)
create_free(blockSize[i]);
for (int i = 0; i < n; i++)
create_alloc(processSize[i]);
print_alloc();
// block of tag id 1 deleted
// to free space for block of size 426
delete_alloc(1);
create_alloc(426);
Console.WriteLine("After deleting block"
+ " with tag id 1.");
print_alloc();
}
}
// Javascript implementation of program
// for best fit algorithm for memory
// management using linked list
// Two global counters
let g = 0, k = 0;
// Structure for free list
class Free {
constructor(tag, size, next) {
this.tag = tag;
this.size = size;
this.next = next;
}
}
let freeHead = null, prevFree = null;
// Structure for allocated list
class Alloc {
constructor(blockId, tag, size, next) {
this.blockId = blockId;
this.tag = tag;
this.size = size;
this.next = next;
}
}
let allocHead = null, prevAlloc = null;
// Function to create free
// list with given sizes
function createFree(c) {
let p = new Free(g, c, null);
if (freeHead == null) {
freeHead = p;
} else {
prevFree.next = p;
}
prevFree = p;
g++;
}
// Function to print free list which
// prints free blocks of given sizes
function printFree() {
let p = freeHead;
console.log("Tag\tSize");
while (p != null) {
console.log(p.tag + "\t" + p.size);
p = p.next;
}
}
// Function to print allocated list which
// prints allocated blocks and their block ids
function printAlloc() {
let p = allocHead;
console.log("Tag\tBlock ID\tSize");
while (p != null) {
console.log(p.tag + "\t " + p.blockId + "\t\t" + p.size);
p = p.next;
}
}
// Function to allocate memory to
// blocks as per Best fit algorithm
function createAlloc(c) {
// create node for process of given size
let q = new Alloc(null, k, c, null);
let p = freeHead;
// Temporary node r of free
// type to find the best and
// most suitable free node to
// allocate space
let r = new Free(null, 0, null);
r.size = 99999;
// Loop to find best choice
while (p != null) {
if (q.size <= p.size) {
if (p.size < r.size) {
r = p;
}
}
p = p.next;
}
// Node found to allocate
// space from
if (r.size != 99999) {
// Adding node to allocated list
q.blockId = r.tag;
r.size -= q.size;
if (allocHead == null) {
allocHead = q;
} else {
prevAlloc = allocHead;
while (prevAlloc.next != null) {
prevAlloc = prevAlloc.next;
}
prevAlloc.next = q;
}
k++;
}
// Node with size not found
else {
console.log("Block with size " + c + " can't be allocated");
}
}
// Function to delete node from
// allocated list to free some space
function deleteAlloc(t) {
// Standard delete function
// of a linked list node
let p = allocHead, q = null;
// First, find the node according
while (p != null) {
// to given tag id
if (p.tag == t) {
break;
}
q = p;
p = p.next;
}
if (p == null) {
console.log("Tag ID doesn't exist");
} else if (p == allocHead) {
allocHead = allocHead.next;
} else {
q.next = p.next;
}
let temp = freeHead;
while (temp != null) {
if (temp.tag == p.blockId) {
temp.size += p.size;
break;
}
temp = temp.next;
}
}
// Driver Code
function main() {
const blockSize = [100, 500, 200];
const processSize = [95, 417, 112, 426];
const m = blockSize.length;
const n = processSize.length;
for (let i = 0; i < m; i++) {
createFree(blockSize[i]);
}
for (let i = 0; i < n; i++) {
createAlloc(processSize[i]);
}
printAlloc();
// block of tag id 1 deleted
// to free space for block of size 426
deleteAlloc(1);
createAlloc(426);
console.log("After deleting block with tag id 1.");
printAlloc();
}
// this code is contributed by bhardwajji
Output: Block with size 426 can't be allocated
Tag Block ID Size
0 0 95
1 1 417
2 2 112
After deleting block with tag id 1.
Tag Block ID Size
0 0 95
2 2 112
3 1 426
The time complexity of this program is O(m+n) as we traverse the blockSize and processSize array of sizes and create both free and allocated list.
The space complexity is O(m+n) as we create m+n nodes for free and allocated list respectively.
Similar Reads
First Fit algorithm in Memory Management using Linked List
First Fit Algorithm for Memory Management: The first memory partition which is sufficient to accommodate the process is allocated.We have already discussed first fit algorithm using arrays in this article. However, here we are going to look into another approach using a linked list where the deletio
15+ min read
Program for Best Fit algorithm in Memory Management
Prerequisite : Partition allocation methodsBest fit allocates the process to a partition which is the smallest sufficient partition among the free available partitions. Example: Input : blockSize[] = {100, 500, 200, 300, 600}; processSize[] = {212, 417, 112, 426}; Output: Process No. Process Size Bl
8 min read
Program for First Fit algorithm in Memory Management
Prerequisite : Partition Allocation MethodsIn the first fit, the partition is allocated which is first sufficient from the top of Main Memory.Example : Input : blockSize[] = {100, 500, 200, 300, 600}; processSize[] = {212, 417, 112, 426};Output:Process No. Process Size Block no. 1 212 2 2 417 5 3 11
8 min read
Program for Worst Fit algorithm in Memory Management
Prerequisite : Partition allocation methodsWorst Fit allocates a process to the partition which is largest sufficient among the freely available partitions available in the main memory. If a large process comes at a later stage, then memory will not have space to accommodate it. Example: Input : blo
8 min read
Menu driven program for all operations on singly linked list in C
A Linked List is a linear data structure that consists of two parts: one is the data part and the other is the address part. In this article, all the common operations of a singly linked list are discussed in one menu-driven program.Operations to be PerformedcreateList(): To create the list with the
8 min read
Best Fit Memory Management in Python
Memory management is a critical aspect of any programming language, and Python is no exception. While Python’s built-in memory management is highly efficient for most applications, understanding memory management techniques like the Best Fit strategy can be beneficial, especially from a Data Structu
4 min read
Implementation of First Fit Memory Management in Python
First Fit memory management is a technique used in operating systems for allocating memory to processes. When a process requests memory, the allocator searches the available memory blocks from the beginning of the memory and allocates the first block that is large enough to accommodate the process.
2 min read
Find the Largest Number Using Four Nodes in a Singly Linked List
Given a singly linked list, the task is to find the largest number in the linked list using four nodes. Examples: Input: List: 2->5->3->4->6Output: 6543Explanation: Using the four nodes, we traverse the linked list and construct the largest number, which is 6543 Input: List: 1->7->
12 min read
Introduction to Linked List - Data Structure and Algorithm Tutorials
Linked List is basically chains of nodes where each node contains information such as data and a pointer to the next node in the chain. It is a popular data structure with a wide range of real-world applications. Unlike Arrays, Linked List elements are not stored at a contiguous location. In the lin
9 min read
Partition Allocation Methods in Memory Management
In the operating system, the following are four common memory management techniques. Single contiguous allocation: Simplest allocation method used by MS-DOS. All memory (except some reserved for OS) is available to a process. Partitioned allocation: Memory is divided into different blocks or partiti
4 min read