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Custom Malloc and Free

This library provides a custom implementation of memory allocation (my_malloc) and deallocation (my_free) using a doubly-linked list of memory blocks. The primary goal is to manage memory dynamically, allowing users to allocate and free memory as needed.

Features

  • Memory Allocation: The my_malloc function allocates memory blocks, searching for a suitable free block or splitting a larger block using the first-fit algorithm.

  • Memory Deallocation: The my_free function marks a previously allocated block as free and coalseces adjacent free blocks to optimize memory usage.

  • Initialization: The mem_init function initializes the custom memory allocation library by allocating a main memory block and intializing the linked list.

Why First Fit?

The memory allocation strategy used in this code is the "first-fit" algorithm, where the first available block that satisfies the allocation size is chosen. This strategy is a simple methodology where the suitable free block in the list is used, as opposed to the best-fit, improving runtime at the cost of slight external fragmentation.

First-Fit Diagram:

First-Fit Diagram

In this example diagram, an item of size 500 is attempting to be allocated within a memory block featuring three open blocks of sizes 1000, 2000, and 550. The first fit algorithm selects the first available block with sufficient space (in this case, the 1000-sized block) for the requested item. Any extra space will be split into a new free block.

What is Coalescing?

Coalescing is a memory management technique used to merge adjacent free blocks into a single, larger free block. This helps prevent external memory fragmentation and ensures more efficient use of available memory. As the inital memory block is used up however, coalescing becomes less effective.

Coalescing Diagram:

Coalescing Diagram

The 'Before Coalescing' diagram depicts a memory layout with alternating allocated and free blocks, in the strucutre of a linked list. After applying memory coalescing, represented in the 'After Coalescing' diagram, adjacent free blocks are merged to create a more contiguous and efficient memory space. This process is done everytime my_free is called, minimizing external fragmentation.

Installation and Use

  1. Clone the repository to your local machine:

    git clone https://github.com/Daksh2060/custom-malloc-free-c.git

  2. If using the provided test file, simply run using the included make file:

    make
./mem_test

    To use in your own program, include the library header in your C file:

    #include "my_malloc.h"

  3. To adjust the maximum size of the allocated block, adjust TOTAL_BLOCK value within my_malloc.h:

    #define TOTAL_BLOCK 1000

  4. Initiate the library within main():

    mem_init();

  5. To use allocated memory, call as you would malloc, for example, to allocate a single int:

    int* int1 = (int*)my_malloc(sizeof(int));

  6. To free memory, call as you would free:

    my_free(int1);

  7. Free the inital memory block at the very end of your program to clean up:

    free_block();

Contact

Feel free to reach out if you have any questions, suggestions, or feedback: