This bug was fixed in the package lxcfs - 3.0.3-0ubuntu1~18.04.2
---------------
lxcfs (3.0.3-0ubuntu1~18.04.2) bionic; urgency=medium
* d/p/0001-better-handle-swapfree-calculation.patch: (LP: #1860813)
- bindings: fix swapFree calculation with swap accounting enabled
-- Kellen Renshaw <kellen.rens...@canonical.com> Tue, 31 Mar 2020
16:20:51 +0000
** Changed in: lxcfs (Ubuntu Bionic)
Status: Fix Committed => Fix Released
** Changed in: lxcfs (Ubuntu Eoan)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1860813
Title:
LXC container reports spike in swap occasionally
Status in lxcfs package in Ubuntu:
Fix Released
Status in lxcfs source package in Xenial:
Invalid
Status in lxcfs source package in Bionic:
Fix Released
Status in lxcfs source package in Eoan:
Fix Released
Bug description:
[Impact]
* lxcfs provides a container-specific view of /proc/meminfo.
Occasionally, with near zero or zero swap usage *and* swap accounting
turned on (kernel parameter swapaccount=1), the container will report
100% swap utilization.
* This issue has been encountered and could result in unecessary
alerts or potential automated attempts at remediating a non-existent
"full swap" issue.
* This fix changed the logic used for SwapFree when swap accounting
is enabled to better handle situations where memswusage is less than
memusage, caused by the fuzziness of the usage_in_bytes counters used
as the source. Specifically, it added a check for memusage being
larger than memswusage and if so, sets 0 as the value of swapusage.
Otherwise the calculation (memswusage - memusage) remains the same.
[Test Case]
* Requires a Bionic (18.04) or Eoan (19.10) host with swap space.
* Enable swap accounting with the "swapaccount=1" kernel parameter on
the kernel command line. Edit /etc/default/grub, add "swapaccount=1"
to the GRUB_CMDLINE_LINUX_DEFAULT="other parameters" line, then run
"update-grub" and reboot to make the change active.
* Ensure lxd is installed, "sudo apt install lxd"
* Create a lxd/lxc container with "lxc launch ubuntu:X
container_name" with X being either b[ionic] or e[oan].
* Open two shells to the container with "lxc shell container_name"
* In one of the shells, run: watch -n 0.1 "grep Swap /proc/meminfo"
* In the other, run: while true; do free; done
* You should see SwapFree intermittently drop to zero in the first
terminal.
* The fix results in small non-zero swap "usage" intermittently
instead of intermittent SwapFree = 0.
[Regression Potential]
* Low, as swap accounting must be enabled to encounter the bug and
the fix.
* Potential for unanticipated edge cases in the values of memusage
and memswusage to cause incorrect swap reporting within the container,
with swap accounting turned on.
* Any tooling that expected, compensated, or relied on the behavior
may no longer work as expected.
[Other Info]
* Cherrypick of a one line fix to address this specific situation.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/lxcfs/+bug/1860813/+subscriptions
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