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Asked: 2025-05-21T14:14:29+05:30

Is it better to use stack memory or a Memory Arena for storing large game structs like Entities and MapData?

I’ve been diving into memory management lately, especially in the context of game development, and I’m stuck on a decision about how to properly store my large structs like Entities and MapData. My current approach has been to use stack memory for these entities, but I’m starting to second-guess that choice.

Check this out: I have this `Entities` struct, which has a fixed size array for various attributes like bounding boxes, colors, types, speeds, and health meters for 51 entities. The entity empty slots and occupied slots are stored as separate `IntArr` structs. Since these entities are crucial for gameplay and exist for the entire run-time of the game, I feel like they might be better suited for heap allocation, particularly using a Memory Arena.

From what I understand, using stack memory is great for quick allocations and deallocations, but it has its limitations. Since the `Entities` struct is quite large and might need to persist throughout the game, should I really be keeping it on the stack? Is stack overflow a risk if I have multiple instances of this struct or work with other large data?

I’m leaning towards moving my `Entities` struct to a Memory Arena since it would give me more control over memory allocation, potentially avoid fragmentation, and help me manage the lifecycle of these entities more effectively. Plus, with the arena, I wouldn’t have to worry much about the cleanup for each individual entity after its lifespan ends.

However, I’m curious about other devs’ experiences. Is using a Memory Arena overkill for something like an entity pool? Have you run into issues with performance when switching from stack to heap memory for large data types? Are there specific scenarios where stack memory would have an advantage over heap memory, especially for structs that are as large as this one? Looking forward to hearing your thoughts!

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    2 Answers

    1. Hey there! It sounds like you’re diving deep into some pretty interesting stuff with memory management, especially for game dev. So, you’ve got this `Entities` struct that’s quite sizable, and you’re using stack memory for it? I totally get why you’re second-guessing that choice!

      The stack is indeed super fast for allocations and is great when you have temporary data, but as you mentioned, it doesn’t handle larger or persistent data really well. Stack overflow could definitely be a risk if your `Entities` struct takes up a lot of space and you’re trying to do more stuff on the stack at the same time.

      Shifting to a Memory Arena sounds like a solid plan! It would free you from the potential worries of stack overflow and give you more control over memory during the game. Plus, the fact that you can allocate a bunch of entities all at once and then just clean up later seems like a huge win, especially for managing the lifecycle of entities that need to stick around.

      From what I’ve heard, using a Memory Arena isn’t overkill for something like an entity pool at all! A lot of devs find that it simplifies their life, especially with dealing with lots of entities that have the same lifetime. I think the main performance hit when going from stack to heap generally tends to be in allocation speed, but with a well-implemented Memory Arena, you might not even notice much difference.

      In some cases, stack memory might still be beneficial when you’re dealing with smaller structs or temporary data that you’re done with very quickly. It can give you super fast allocations without needing to manage the memory manually. But for something as critical as your `Entities`, it sounds like a smart move to go the arena route.

      Hope this helps you out a bit in figuring things out! Good luck with your game development!

    2. Given the substantial size and prolonged lifetime of your Entities struct, leveraging stack memory might indeed put you at risk of stack overflows, especially if this structure becomes larger or numerous instances are created. Stack memory is ideal for smaller, short-lived variables where quick allocation and deallocation benefit performance. In your scenario, where the entities persist throughout the game’s lifetime and occupy considerable space, a stack allocation approach typically becomes problematic. Transitioning to a heap-allocated memory arena provides not only safety against potential overflows but also facilitates better control over allocation and deallocation cycles, minimizing fragmentation and simplifying lifetime management.

      Although memory arenas do introduce a minor overhead due to the additional indirection and management logic, this overhead is often negligible compared to the improved flexibility and safety they offer for long-lived, large-scale data structures. For extensive entity pools or map data, arenas commonly boost game stability and overall performance by organizing memory more predictably. Nonetheless, the stack memory approach retains an advantage when handling small, temporary data structures where high allocation speed is paramount, such as short-term calculations or quick event-driven processes. Ultimately, utilizing a memory arena for large, persistent structures like your Entities struct appears justified and prudent, aligning well with typical game development best practices.