swapspace grows with no return
Doug Denault
doug at safeport.com
Sun Aug 9 16:52:42 UTC 2020
This is a smallish server, 8G memory, normally running 8 jails. When this
issue started I stopped three of the jails which were used for testing and
development. What's left are jails running apache 2.4, wordpress, and MySQL
5.7. One jail, camden is testing a new version of squirrelmail and
roundcube.
>From swapinfo and top:
Device 1K-blocks Used Avail Capacity
/dev/aacd0p3 4194304 831572 3362732 20%
[ 0, 2010408] root
[13, 3359976] camden
[15, 5039344] bassharbor
[14, 5201500] monhegan
[12, 5776608] newharbor
[ 4, 6870432] pemaquid
total: 28258268
So about 3% of the virtual storage allocated is currently written to the
swap file. Two times in the last several weeks the swap file has run out of
space. This is Sunday, there is as close to zero activity as these guys
get. The 20% will only grow from here.
I ran vmstat over night; there were about 10 pageins and no pageouts. top
and 'systat vmstat' also show no paging. The swap file when from 18% to 20%
over that time frame. The obvious question is: how come?
sysctl swap counts:
vm.swap_enabled: 1
vm.disable_swapspace_pageouts: 0
vm.swap_idle_enabled: 0
vm.stats.vm.v_swappgsout: 631602
vm.stats.vm.v_swappgsin: 46818
vm.stats.vm.v_swapout: 53454
vm.stats.vm.v_swapin: 9842
vm.swap_idle_threshold2: 10
vm.swap_idle_threshold1: 2
vm.nswapdev: 1
vm.swap_async_max: 4
vm.swap_maxpages: 32444512
vm.swap_reserved: 30920429568
vm.swap_total: 4294967296
Seems ok to me. We had to reboot about five days ago. Twice since then we
just rebooted the offending jail.
Past what is going on: The default installation will allocate a 4G
swapfile. I am pretty sure I read from a FreeBSD source that the 2 x
physical memory rule is not needed. Several threads on questions suggest
otherwise. What is the 'best practice' here?
I also read somewhere that the VM system will preactively pageout changed
pages. That would seem to be the case here, but they are never freed.
Lastly, can an application lock memory?
Thanks for any suggestions,
Doug
_____
Douglas Denault
http://www.safeport.com
doug at safeport.com
Voice: 301-217-9220
Fax: 301-217-9277
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