Memory Allocator

A simple yet powerful dynamic memory management system that mimics the behavior of malloc, free, calloc, and realloc, tailored for both small and large memory allocations.

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Features

• Custom malloc, free, calloc, realloc functions using data structures
• Memory coalescing to reduce fragmentation
• Block splitting for efficient space use
• Separate strategies for small & large allocations

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Usage

Include the header and link the implementation file:

#include "osmem.h"

Then use the custom allocation functions just like standard ones:

void *ptr = os_malloc(64);
os_free(ptr);

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Functions

void *os_malloc(size_t size)

Allocates a block of memory of the specified size.
Uses internal data structures to track and deliver usable payloads.

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void os_free(void *ptr)

Frees the memory block pointed to by ptr.
Handles both sbrk-based and mmap-based memory allocations.

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void *os_calloc(size_t nmemb, size_t size)

Allocates memory for an array and initializes it to zero.
Perfect for ensuring clean, zeroed memory.

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void *os_realloc(void *ptr, size_t size)

Resizes a previously allocated block.
Handles all edge cases like expansion, shrinking, or creating new blocks.

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Memory Allocation Strategies

Small Allocations (< CHUNK size)

• Uses sbrk syscall for linear heap expansion.
• Preallocates a chunk on first use.
• Finds suitable free blocks or expands the heap.

Large Allocations (>= CHUNK size)

• Uses mmap syscall for direct mapping of large memory blocks.

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Optimizations

Memory Coalescing

Adjacent free blocks are merged to prevent fragmentation.

Block Splitting

Large blocks are split into smaller parts when possible.

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📁 File Structure

├── osmem.h         # Header file with function declarations
├── osmem.c         # Implementation of the memory allocator
└── README.md       # You are here!