Custom Arena Allocator in C

A custom arena memory allocator written from scratch in C as a low-level memory-management learning project.

What Is an Arena Allocator?

An arena allocator is a memory allocation strategy where a large region of memory is obtained once and smaller allocations are made from that region.

Instead of individually allocating and freeing every object, the arena maintains a current position and moves that position forward as allocations are requested.

For more background on arena allocators: https://www.dgtlgrove.com/p/untangling-lifetimes-the-arena-allocator

Current Implementation

This version of the arena allocator uses malloc() as its underlying memory source.

The arena first allocates memory for the arena structure itself and then allocates a contiguous memory buffer using malloc():

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Custom Virtual Memory Arena Allocator in C

A custom arena memory allocator written from scratch in C as a low-level memory-management learning project.

This is the second version of my arena allocator. Unlike the first version, this implementation uses virtual memory reservation and commitment instead of using malloc() for the main arena memory buffer.

Version 2 — Virtual Memory Arena using mmap()

This version goes one level lower and uses the operating system's virtual memory facilities.

The arena first reserves a large virtual address range and initially commits only a small portion of that range.

arena_create()

     │
     ├── malloc(sizeof(arena))
     │
     └── reserve virtual address space
              │
              ▼
        ┌──────────────────────────────┐
        │      Reserved Address Space  │
        │                              │
        │  ┌──────────────┐            │
        │  │   Committed  │            │
        │  │    Memory    │            │
        │  └──────────────┘            │
        │                              │
        │       Reserved               │
        │       but not                │
        │       committed              │
        │                              │
        └──────────────────────────────┘