memory-allocator

Custom malloc, free, calloc and realloc implementations using sbrk and mmap syscalls, with best-fit allocation, block splitting, block coalescing and heap preallocation

Overview

• This project implements a memory allocator that manages heap memory through a doubly-linked list of memory blocks. It mimics the behavior of the standard C library allocator with manual control over memory allocation strategies.

Features

• Dual allocation strategy
  • sbrk for small allocations (< 128 KB)
  • mmap for large allocations (≥ 128 KB)
• Block splitting: splits free blocks when the remaining space is ≥ 40 bytes, reducing internal fragmentation
• Block coalescing: merges adjacent free blocks to reduce external fragmentation
• Best-fit allocation: searches for the smallest free block that satisfies the request
• Heap preallocation: preallocates 128 KB on the first small allocation to minimize sbrk syscalls
• 8-byte alignment: all allocations are padded to 8-byte boundaries

Function ~ Description

• void *os_malloc(size_t size) ~ Allocates "size" bytes of memory
• void os_free(void *ptr) ~ Frees a previously allocated block
• void *os_calloc(size_t nmemb, size_t size) ~ Allocates and zero-initializes memory for an array
• void *os_realloc(void *ptr, size_t size) ~ Resizes a previously allocated block

Usage

#include "osmem.h" int main() { int *arr = os_malloc(10 * sizeof(int)); for (int i = 0; i < 10; i++) arr[i] = i; arr = os_realloc(arr, 20 * sizeof(int)); os_free(arr); return 0; }