ARC size constantly shrinks, then ZFS slows down extremely

[Pawel Jakub Dawidek]

On Fri, Oct 02, 2009 at 04:38:24PM -0700, Artem Belevich wrote:
> With the patch, if vfs.zfs.arc_min is set high enough, the system locks up.
> 
> On a box with 8G or RAM I had arc_min=6G and arc_max=7G. Once ARC grew
> to ~5.8G as reported by kstat.zfs.misc.arcstats.size, number of wired
> pages grew to ~7400MB and the processes got stuck in 'vmwait' state. I
> had to reboot in order to recover.
> 
> On one hand setting arc_min can be considered a pilot error. On the
> other, it may be a good idea to allow system to reclaim memory from
> ARC even if ARC is smaller than arc_min if the system really really
> needs it. The question is how to define "really needs it".
> 
> On a side note, it appears that wired page count tends to be
> substantially larger than ARC size. I.e. in my case if ARC size grows
> to 6G, wired page count is about 1.5G bigger. Perhaps we should allow
> reclaiming memory

Before we start debuging pathological cases, could you try the patch
with defaul settings? Eventually with vm.kmem_size set to the amount of
RAM you have.

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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