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** Changed in: linux (Ubuntu)
Status: New => Incomplete
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https://bugs.launchpad.net/bugs/1666683
Title:
Default VM overcommit sysctls in Ubuntu lead to unnecessary oom-killer
invocation
Status in linux package in Ubuntu:
Incomplete
Bug description:
On my system, running a couple of LXD containers and VMs (16 GB RAM,
16 GB swap) seems to cause the kernel oom-killer to be frequently
triggered.
In order to try to resolve this, first I tried limiting the memory my
containers were allowed to use, such as by using:
lxc config set <container> limits.memory 1024GB
... and restarting the containers for good measure. However, this
didn't resolve the problem.
After looking deeper into what might trigger the oom-killer even
though I seemed to have plenty of memory free, I found out that the
kernel VM overcommit can be tuned with the `vm.overcommit_memory`
sysctl.
The default for value of `vm.overcommit_memory`, 0, uses a heuristic
to determine whether or not requested memory is available. According
to the `man 5 proc`, if the value is set to zero:
"""
calls of mmap(2) with MAP_NORESERVE are not checked, and the
default check is very weak, leading to the risk of getting a
process "OOM-killed".
"""
Which seems to describe exactly my problem. However, upon setting this
value to 2, many of my open programs immediately aborted with out-of-
memory errors. This is because the default value for
`vm.overcommit_ratio` only allows the usage of 50% of the system's
total (memory + swap).
I then found the following answer on Server Fault:
http://serverfault.com/a/510857/15268
The answers to this question seem to make a good case that the
overcommit_ratio should be set to 100.
In summary, I think the following sysctl values should be the new
defaults:
vm.overcommit_memory = 2
vm.overcommit_ratio = 100
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