I think that a blanket should/shouldn't recommendation for arenas isn't right. Arenas are a tradeoff:
Pros: preallocating one arena is likely faster than many smaller allocations.
Cons: preallocation is most effective if you can accurately predict usage for the arena; if you can't, then you either overshoot and allocate more memory than you need, or undershoot and have to reallocate which might be less performant than just allocating as-needed.
In short, if you're preallocating, I think decisions need to be made based on performance testing and the requirements of your program (is memory usage more important than speed?). If you aren't preallocating and just using arenas for to free in a group, then I'm going to say using an arena for stuff that is going to be freed by the OS at program exit is adding complexity for no benefit--it depends on your arena implementation (arenas aren't in the C standard to my knowledge).
In general, I'd be erring on the side of simplicity here and not using arenas for this by default--I'd only consider adding arenas if performance testing shows the program spending a lot of time in individual allocations. So I don't think a blanket recommendation for arenas is a good idea here.
EDIT: In case it's not obvious: note that I'm assuming that the reason you want to use an arena is to preallocate. If you're thinking that you're going to call free on the arena on program exit, that's just as pointless as calling free on a bunch of individual allocations on program exit. It MIGHT be faster, but doing pointless things faster is still not as good as not doing pointless things.
alt Hacker News
I think that a blanket should/shouldn't recommendation for arenas isn't right. Arenas are a tradeoff:
Pros: preallocating one arena is likely faster than many smaller allocations.
Cons: preallocation is most effective if you can accurately predict usage for the arena; if you can't, then you either overshoot and allocate more memory than you need, or undershoot and have to reallocate which might be less performant than just allocating as-needed.
In short, if you're preallocating, I think decisions need to be made based on performance testing and the requirements of your program (is memory usage more important than speed?). If you aren't preallocating and just using arenas for to free in a group, then I'm going to say using an arena for stuff that is going to be freed by the OS at program exit is adding complexity for no benefit--it depends on your arena implementation (arenas aren't in the C standard to my knowledge).
In general, I'd be erring on the side of simplicity here and not using arenas for this by default--I'd only consider adding arenas if performance testing shows the program spending a lot of time in individual allocations. So I don't think a blanket recommendation for arenas is a good idea here.
EDIT: In case it's not obvious: note that I'm assuming that the reason you want to use an arena is to preallocate. If you're thinking that you're going to call free on the arena on program exit, that's just as pointless as calling free on a bunch of individual allocations on program exit. It MIGHT be faster, but doing pointless things faster is still not as good as not doing pointless things.