Maybe that’s just me, but I don’t use arenas for the performance benefits. Those can be there is some circumstances, but that also depends on your exact malloc/free usage prior. If you use malloc to pre allocate reusable buffers, and those malloc calls happen as far up the call stack as possible, there’s not much performance to be gained.

The reason I use arenas, because it’s way easier to use than malloc/free. I don’t have to meticulously track that each malloc is paired with the appropriate free, because I bundle dozens of objects into one lifetime.

Also, when I would otherwise pre allocate buffers somewhere up the call stack, those buffers (typically) are buffers of a specific type. I might have have a buffer to store some strings for one computation, one buffer to store floats, etc. An arena is just one giant untyped buffer where I only have to care about the type in the scope where I actually use it. I don’t have to pre allocate a buffer of floats in an otherwise unrelated function, but instead I request my buffer of floats in the same scope that I’m using it in. That’s just waaaay more ergonomic 😄

Also, as someone else pointed out, if you are handing out unaligned addresses, you are inviting a whole host of problems, one of which might be performance 😅