Differences in memory handling on systems with/out cache drives

[Karli Sjöberg]

On Wed, 2014-11-05 at 16:36 +0100, Erik Stian Tefre wrote:
> On 05. nov. 2014 09:53, Karli Sjöberg wrote:
> > On Wed, 2014-11-05 at 08:44 +0000, Karli Sjöberg wrote:
> >> Hey all!
> >>
> >> Still investigating the intermittent lockups we are experiencing on our
> >> storage systems and have started to compare memory graphs from our
> >> Graphite monitoring system. What´s interesting about two of our systems
> >> is that they both have the same amount of RAM; 32 GB. But on one of
> >> them, I have "zpool remove"'d the cache drives from the pool and have
> >> been able to study how different their memory graphs now look like.
> >>
> >> Also worth noting is that the cache-less system nearly haven´t swapped
> >> at all (1112K) since the last stall 20 days ago, while the other system
> >> has swapped 78 MB during it´s 48 days of uptime.
> >>
> >> I´ve attached both screenshots from the two systems, with- and without
> >> cache drives, displaying a period of 12 hours.
> >>
> >> What´s most notable are the characteristic cuts that happen on the
> >> cache-less system when ZFS goes in and evicts blocks from ARC that shows
> >> as a decrease in "wired" and increase in "free", that just doesn´t
> >> happen/looks different in the system with cache drive configured in the
> >> pool.
> >>
> >> What´s your take on this? Are we hitting bug: 187594 perhaps? How can we
> >> know?
> Take a look at the recent thread on freebsd-stable@, subject "ARC size 
> limit". Possibly related issues have been patched in stable/10, the 
> mailing list thread includes a patch for releng/10.1.

Thanks! I looked at it and saw that that´s one that´s going to be used
for 10.1[1] and the patch referred to is the same as the one developed
for bug 187594[2], which still has status "In Discussion". The patch
really should be verified by OP there before issue is _really_ declared
resolved.

@Karl
Do you have any chance of verifying this, as you were the one that first
reported about it? I would personally feel so much better knowing we can
finally rid ourselves of this menace in 10.1:)

[1]:https://lists.freebsd.org/pipermail/freebsd-stable/2014-November/080894.html
[2]:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=187594#c189


-- 

Med Vänliga Hälsningar

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Karli Sjöberg
Swedish University of Agricultural Sciences Box 7079 (Visiting Address
Kronåsvägen 8)
S-750 07 Uppsala, Sweden
Phone:  +46-(0)18-67 15 66
karli.sjoberg at slu.se