zio unused UMA zones

[Davide Italiano]

Hi.
Looking at vmstat -z I saw zones zio_buf and zio_data_buf are created
even if vfs.zfs.zio.use_uma is set to zero.
If UMA is not used for allocating ZFS I/O buffers such zones remain
unused. Is there any reason to create them I'm missing or is this just
an oversight?
In case it's the second choice, do you mind if I modify the code so
that zones are created only if needed?

Thanks,

-- 
Davide