RNrnhmjoj·Oct 6, 2021
The reason the OOM killer never kicks in is because you actually never run into an OOM, or almost never.
What usually happens is that in near-OOM conditions, the kernel starts reclaiming memory pages backed by file (sometimes called "trashing"). This operation manages to keep some extra memory available, but it makes the system almost unresponsive because it's constantly copying memory back and forth from the disk. It may take anywhere between minutes to hours before the system finally OOMs and the OOM killer is invoked.
This problem has been there forever but has been made worse by the improved speeds of modern storage technologies: with slower disk I/O, the OOM condition was reached sooner.
There are several solutions:
- Buy more RAM: if your system routinely goes nearly OOM something is not right.
- Add a (small) swap. It doesn't have
Read the rest
to be a partition: nowadays most filesystems support swap file. Just create an empty file and mark it as swap.
- Limit the amount of thrashing or protect some pages from being reclaimed. This has been proposed by Google first and several other people since then, but AFAIK it has never been implemented in the mainline kernel.
Regarding the latter solution, there is a patchset called le9-patch[1] that is included in some alternative Linux kernels and it should be relatively safe to use.
[1]: https://github.com/hakavlad/le9-patch