Date: Tue, 19 Jun 2018 09:48:26 +0800 From: Erich Dollansky <freebsd.ed.lists@sumeritec.com> To: tech-lists <tech-lists@zyxst.net> Cc: freebsd-stable@freebsd.org, freebsd-questions@freebsd.org Subject: Re: lightly loaded system eats swap space Message-ID: <20180619094826.75c0c735.freebsd.ed.lists@sumeritec.com> In-Reply-To: <ab5d0cb0-13f5-5de8-6189-c0a5c621c6e9@zyxst.net> References: <c8277497-ffcf-0503-490b-96d1b4605af7@zyxst.net> <20180618160855.44d9a0c2.freebsd.ed.lists@sumeritec.com> <ab5d0cb0-13f5-5de8-6189-c0a5c621c6e9@zyxst.net>
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Hi, On Mon, 18 Jun 2018 13:27:23 +0100 tech-lists <tech-lists@zyxst.net> wrote: > On 18/06/2018 09:08, Erich Dollansky wrote: > > > > On Sun, 17 Jun 2018 23:19:02 +0100 > > tech-lists <tech-lists@zyxst.net> wrote: > > > >> freebsd-11-stable r333874, ZFS raidz1-0 (3x4TB disks), 128GB RAM, > >> Swap: 4096M Total, 3502M Used, 594M Free, 85% Inuse > > > > this might not be related but I noticed that your swap space is > > small compared to RAM size. I noticed on a much smaller Raspberry > > Pi, that it runs into trouble when there is no swap even there is > > enough RAM available. Is it easily possible for you to add some GB > > of swap space and let the machine run then? > > > > How much swap do the other machines have? > > Yes, the machine with the problem uses the default 4GB swap. That's > all the swap it has. The machine without issue has a swapfile > installed on a SSD in addition to the default 4GB swap. > > problematic machine: > Device 512-blocks Used Avail Capacity > /dev/ada0p3 8388608 3.3G 714M 83% > > machine without a problem, it has swapfile installed: > Device 512-blocks Used Avail Capacity > /dev/ada0s1b 8262248 1.7G 2.2G 44% > /dev/md0 65536000 1.9G 29G 6% > Total 73798248 3.7G 32G 10% > > I added the swapfile a long time ago on this machine due to the same > issue. so, the same effect as on a small Raspberry. It seems that you also use a memory disk for swap. Mine is backed by a file via NFS. > > But my problem isn't so much an out of swapspace problem; all this > is, is a symptom. My problem is "why is it swapping out at all on a > 128GB system and why is what's swapped out not being swapped back in > again". > I wondered even on the small Raspberry about this. The Raspberries come with 1GB of RAM. Running just a compilation should never be the problem but sometimes it is. A very long time ago - and not on FreeBSD but maybe on a real BSD - I worked with a system that swapped pages out just to bring it back as one contiguous block. This made a difference those days. I do not know if the code made it out of the university I was working at. I just imagine now that the code made it out and is still in use with the opposite effect. Erich
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