zio unused UMA zones

[Davide Italiano]

On Sat, Apr 20, 2013 at 11:07 PM, Pawel Jakub Dawidek <pjd at freebsd.org> wrote:
> On Fri, Apr 19, 2013 at 01:22:57PM +0200, Davide Italiano wrote:
>> 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?
>
> The only reason I can think of to leave those zone around is ability to
> switch between UMA-allocated buffers and malloc-allocated buffers at
> runtime, but currently I don't think this is possible (we would be able
> to tell how the given buffer was allocated), so most likely I first
> implemented this by using UMA, but when problems with KVA fragmentation
> appeared I added a switch to use malloc and haven't made UMA zones
> creations to depend on this switch.
>
> I'd be happy to review the patch.
>
> --
> Pawel Jakub Dawidek                       http://www.wheelsystems.com
> FreeBSD committer                         http://www.FreeBSD.org
> Am I Evil? Yes, I Am!                     http://mobter.com

This should suffice, I guess

http://people.freebsd.org/~davide/review/zfs_noumacreate.diff

Thanks,

-- 
Davide

"There are no solved problems; there are only problems that are more
or less solved" -- Henri Poincare