Minimal Memory Allocator

This project is a minimalist implementation of a custom memory allocator, providing core functions like malloc, calloc, realloc, and free for Linux systems. Its goal is to offer a practical understanding of virtual memory management, fragmentation techniques, and system call optimization.

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Implemented Features

The allocator manages memory using a linked list of memory blocks (struct block_meta) and leverages specific Linux system calls:

• brk/sbrk: Used for small heap allocations (below the MMAP_THRESHOLD).
• mmap/munmap: Used for large allocations (equal to or greater than MMAP_THRESHOLD).
• 8-byte Alignment: All allocations and metadata structures are 8-byte aligned for efficiency and portability on 64-bit systems.
• Heap Preallocation: The first small allocation triggers a large 128 KiB allocation to reduce subsequent brk/sbrk calls.
• Best Fit Strategy: When searching for free memory, the smallest available free block that can satisfy the request is chosen.
• Coalescing: Adjacent free blocks are merged (in os_free and os_realloc) to reduce external fragmentation.
• Splitting: Large free blocks are split to match the requested size, turning the remainder into a new free block to reduce internal fragmentation.
• In-Place realloc: os_realloc attempts to expand the block in place on the heap (including by coalescing with free neighbors) before moving the data.

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🛠️]Block Structure

Every allocated memory zone is preceded by its metadata structure, which is also 8-byte aligned.

// Block metadata definition
struct block_meta {
    size_t size;
    int status; // STATUS_FREE, STATUS_ALLOC, STATUS_MAPPED
    struct block_meta *prev;
    struct block_meta *next;
};