zio unused UMA zones

[Pawel Jakub Dawidek]

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
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