is TMPFS still highly experimental?

[Artem Belevich]

On Mon, Oct 3, 2011 at 11:33 AM, Attila Nagy <bra at fsn.hu> wrote:
> Sounds plausible. BTW, it may be possible that the ARC limits are not needed
> anymore, they are here from the times, where on a 64 GB machine ARC hovered
> around 2-5 GBs without setting these (arc_min was even higher then).

You do need tuning. FreeBSD defaults are way too conservative for ZFS.
While they may get you a working ZFS config, you will end up with ARC
using only small fraction of your memory, which is probably not the
best setup for a filesrever.

> BTW, the user space programs fit into around 1-2 GB RAM on this machine
> typically. Well, most of the time. :)

Yup. 2GB for apps, 2-5GB for ZFS ARC and you end up with 50+GB of
memory that's effectively wasted. The trick is in finding the balance
where ZFS uses as much memory as you can give it without causing
trouble for other subsystems. ARC back-pressure mechanism works
somewhat better now than it used to, but it's still very far from
perfect. Ideally it would be nice to integrate ARC with the FreeBSD's
unified cache, but that's not a trivial task, as far as I can tell.

--Artem

>>
>> I'd start with doubling kmem_size and, possibly, reducing arc_max to
>> the point where it stops putting pressure on tmpfs.
>>
> I know there are several differences, but it would be very good to have
> similar behaviour with UFS. I guess it's quite evident that tmpfs can eat
> the file system cache, and I know it may be not so trivial to solve this
> with ZFS. :)
>
> Will try it, thanks.
>