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++ 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 |
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.