Arena allocator tips and tricks
Having to decide ahead of time how much memory to allocate to the arena is...   crap...The vast majority of programmers don't want arbitrary 'out of memory in arena' errors just because the user inputted slightly more things than expected.     Yes, I know that modern OS's don't actually allocate memory till you use it, but when you make widespread use of that functionality, typically your reuse of address space is poor and free'd stuff will be neither reused nor returned to the OS.Likewise, not being able to free things within the arena is also crap - I'm sure there will be plenty of times the system is running low of RAM, but hundreds of applications have thousands of arenas, all half full of never-to-be-used again items that the OS can't reuse.