Re: ZFS tunable parameters

[Brad Spencer <brad%anduin.eldar.org@localhost>]

Greg Troxel <gdt%lexort.com@localhost> writes:

[snip]

> First, I want to be clear that I welcome Sotiris's efforts to make
> tunables observable and controllable. which I think is good regardless
> of hang issues.
>
> If you are willing, I suggest trying to run stock current in terms of
> the ARC etc. settings.   I think it's reasonably likely things will be
> ok, and whether they are or aren't is a really useful datapoint.

I could not agree more that this is the next test and I spent the last
couple of days doing that.

> ZFS doctrine is to use a lot for the ARC, and to free it on memory
> pressure.  This works fine in Solaris and FreeBSD (idk about Linux where
> ZFS is not first class).  In NetBSD we have had deadlocks -- or maybe
> just missing wakeups -- under memory pressure.

I left the ARC setting stock and performed my usual abuse build testing
and I can say with certainly that it performed as one would expect.  No
lock ups and while swapping was higher than with the adjustments
mentioned in the patch, that would have been expected.  The system
performed perfectly under pretty high memory pressure.

>>> My guess is that reducing arc is a workaround, not a fix, and is
>>> avoiding the locking bugs by leaving more free.  Still, not crashing is
>>> good....   I don't mean to say we shouldn't merge the patch, or that it
>>> isn't helpful to be able to set/observe -- only that there is deeper
>>> trouble.
>>
>> In as much as I was able to tell, the hangs I saw mostly had to do with
>> running out of some sort of memory in a way that the system could not
>> recover from or could not prevent.  This was the first time in a very
>> long time that I was able to push the build system as hard as I wanted
>> to.
>
> Agreed, but I would like to know if it's reduced ARC size or the fixes.

I think I can say, at this point, that the fixes worked and worked very
well.

This is a very welcome change and brings the experience of using ZFS
with NetBSD very close to what you could expect with Solaris.  There are
likely more problems, in the form of missing support, still present with
ZFS, expecially around failed devices, but in -current it works very
well now with far fewer quirks.

Thanks to everyone who made this a reality.





-- 
Brad Spencer - brad%anduin.eldar.org@localhost