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 countersint g = 0, k = 0;// Structure for free liststruct free { int tag; int size; struct free* next;}* free_head = NULL, *prev_free = NULL;// Structure for allocated liststruct alloc { int block_id; int tag; int size; struct alloc* next;}* alloc_head = NULL, *prev_alloc = NULL;// Function to create free// list with given sizesvoid 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 sizesvoid 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 idsvoid 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 algorithmvoid 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 spacevoid 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 Codeint 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
# Python3 implementation of the First# sit memory management algorithm# using linked list# Two global countersg = 0; k = 0# Structure for free listclass free: def __init__(self): self.tag=-1 self.size=0 self.next=Nonefree_head = None; prev_free = None# Structure for allocated listclass alloc: def __init__(self): self.block_id=-1 self.tag=-1 self.size=0 self.next=Nonealloc_head = None;prev_alloc = None# Function to create free# list with given sizesdef 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 sizesdef 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 idsdef 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 algorithmdef 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 spacedef 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 Codeif __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
// Java implementation of program// for best fit algorithm for memory// management using linked listimport java.util.*;// Class for free listclass Free { int tag; int size; Free next; public Free(int tag, int size) { this.tag = tag; this.size = size; next = null; }}// Class for allocated listclass 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#
// C# implementation of program// for best fit algorithm for memory// management using linked listusing System;// Class for free listclass 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 listclass 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
// Javascript implementation of program// for best fit algorithm for memory// management using linked list// Two global counterslet g = 0, k = 0;// Structure for free listclass Free { constructor(tag, size, next) { this.tag = tag; this.size = size; this.next = next; }}let freeHead = null, prevFree = null;// Structure for allocated listclass 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 sizesfunction 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 sizesfunction 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 idsfunction 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 algorithmfunction 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 spacefunction 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 Codefunction 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.
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