gpalmer at freebsd.org
Wed Dec 13 11:23:49 UTC 2017
On Wed, Dec 13, 2017 at 10:34:02AM +0800, blubee blubeeme wrote:
> On Wed, Dec 13, 2017 at 5:53 AM, Mark Millard <markmi at dsl-only.net> wrote:
> > blubee blubeeme gurenchan at gmail.com wrote on
> > Tue Dec 12 15:58:19 UTC 2017 :
> > > On Tue, Dec 12, 2017 at 3:34 PM, blubee blubeeme <gurenchan at gmail.com
> > > >wrote:
> > > > I am seeing tons of these messages while running tail -f
> > /var/log/messages
> > > > ============
> > > > Dec 12 15:11:41 blubee kernel: swap_pager_getswapspace(25): failed
> > > . . .
> > > > 1159 blubee 5 20 0 149M 56876K select 6 1:05 0.00%
> > > > ibus-engine-chewing
> > > >
> > > > ===========
> > > >
> > > > What's with all the swap errors? I am running ZFS and I have 16GB of
> > ram,
> > > > how could I be having swap space errors?
> > > >
> > >
> > > Well I added 4GB of extra swap in /var/tmp/swap0
> > > then added that to my /etc/fstab: md99 none swap
> > > sw,file=/var/tmp/swap0,late 0 0
> > >
> > > and those errors went away.
> > I recommend reviewing bugzilla 206048 (title in part
> > "swapfile usage hangs; swap partition works"):
> > https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=206048
> > before using file-system based swap spaces. They have
> > lots of problems with deadlocks. See especially comments
> > #7 and #8 quoting Konstantin Belousov. #8 is just a
> > reference to:
> > https://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/
> > kerneldebug-deadlocks.html
> > Comment #3 shows a way to test for the problematical
> > behavior.
> > Using swap partitions avoids the issue.
> > ===
> > Mark Millard
> > markmi at dsl-only.net
> Thanks for the info, why would I be getting swap errors like that when I
> have 32GB of ram?
> sysctl hw.physmem
> hw.physmem: 34253692928
> That really doesn't make any sense to me... Is it Chromium eating up 32GB+
> of ram?
Your top output from the first message in the thread gives a hint:
Mem: 3442M Active, 293M Inact, 4901M Laundry, 22G Wired, 1057M Free
ARC: 18G Total, 1488M MFU, 15G MRU, 4003K Anon, 178M Header, 1171M Other
16G Compressed, 23G Uncompressed, 1.41:1 Ratio
Swap: 2048M Total, 2028M Used, 20M Free, 99% Inuse, 36K In
You have 22GB RAM used by the kernel, and 18GB of that is used by ZFS.
As you can see from the last line, 99% of your small swap space is used
and paging was happening at the time of the snapshot ("36K In").
First I would suggest limiting ARC and seeing if that helps. Unless you
are doing a lot of fileserver type work or working with lots of files
you want to keep around that ARC size is a bit big. My desktop with
32GB RAM has ARC limited to 4GB.
Definitely do NOT swap to a file on a filesystem, especially if the
filesystem is ZFS. That will eventually lead to a deadlock.
An open question would be why ARC is not reducing if the system is
under memory pressure. It's meant to, but there have been various
bugs in that implementation.
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