FreeBSD using swap even though there's a lot of free memory
doug at fledge.watson.org
Fri Oct 16 17:50:22 UTC 2020
On Thu, 15 Oct 2020, Jon Schneider wrote:
> top -w -oswap
> seems to report the right thing. Would be interesting if it's _not_ MySQL.
> On 15/10/2020 15:23, Twingly Customer Support wrote:
>> We have a server running FreeBSD 12.1-RELEASE-p10. We currently have a
>> problem where FreeBSD starting to swap when running ZFS scrub, even though
>> we have ~70G of free memory.
>> This did not happen before when running FreeBSD 11.3 for example. It
>> started happening at approximately the time we upgraded from
>> 12.1-RELEASE-p5 to 12.1-RELEASE-p6, but if the upgrade is the cause of the
>> problem is unclear, though FreeBSD never swapped for us before that.
>> "Laundry" memory was not something we saw before either, it started to
>> appear at the same time as FreeBSD started swapping.
>> Eventually, after scrubbing a few times, the swap becomes full and we start
>> seeing "swap_pager_getswapspace(24): failed" etc. in dmesg.
>> This is the memory usage a while after scrubbing, note the values for
>> Mem/Free and Swap:
>> % top | head -n 7
>> last pid: 8112; load averages: 1.82, 1.77, 1.73 up 6+01:37:42
>> 35 processes: 1 running, 34 sleeping
>> CPU: 4.9% user, 0.0% nice, 4.2% system, 0.2% interrupt, 90.7% idle
>> Mem: 110G Active, 27G Inact, 5413M Laundry, 39G Wired, 68G Free
>> ARC: 34G Total, 28G MFU, 4101M MRU, 53M Anon, 1317M Header, 225M Other
>> 30G Compressed, 53G Uncompressed, 1.77:1 Ratio
>> Swap: 8192M Total, 6434M Used, 1757M Free, 78% Inuse
>> We are running MySQL, which has been configured to use ~50% of the total
>> amount memory (using innodb_buffer_pool_size=127748M)
>> ZFS ARC has been configured to use 25% of the total memory (using
>> We have tried raising both vfs.zfs.arc_max and innodb_buffer_pool_size, but
>> this did not make any change to the total memory usage, the free memory
>> stays at around 70G and FreeBSD still started swapping.
>> It's as if the memory is capped at around 180G for some reason.
>> Are there any configuration values that could cause FreeBSD to swap even
>> though there's free memory? Are there any config values one could try to
>> change in order to get FreeBSD to use the remaining ~70G of free memory
>> instead of swapping?
>> Let me know if there's any more details you want me to provide and I'll
>> attach those.
>> // Mattias
I see similar things. The Jails in question are 11.1. The systems updated
to 12.1 do not display this behavior. This 11.1 system runs 5 jails.
Swapinfo is shown below:
Device 1K-blocks Used Avail Capacity
/dev/aacd0p3 4194304 1776000 2418304 42%
These numbers are developed from top on the base system
[ 0 50861 ] root
[ 20 281903 ] camden squirellmail/roundcube/postfix/mysql
[ 21 322759 ] bassharbor wordpress/php56
[ 19 343522 ] monhegan wordpress/php56
[ 18 369139 ] newharbor apache24/sendmail
[ 17 587332 ] pemaquid wordpress/php74
I read somewhere that the virtual memory system pre-pages modified pages as
a just-in-case measure. If this is correct, 12.1 does not do this on a
non-paging system. The system shown above uses about 10% swapspace after a
reboot and works its way to the 42% shown above in a day or so.
More information about the freebsd-questions