Kubernetes OOM pod killed because kernel memory grows to much - docker

Question

I am working on a java service that basically creates files in a network file system to store data. It runs in a k8s cluster in a Ubuntu 18.04 LTS.
When we began to limit the memory in kubernetes (limits: memory: 3Gi), the pods began to be OOMKilled by kubernetes.
At the beginning we thought it was a leak of memory in the java process, but analyzing more deeply we noticed that the problem is the memory of the kernel.
We validated that looking at the file /sys/fs/cgroup/memory/memory.kmem.usage_in_bytes
We isolated the case to only create files (without java) with the DD command like this:
for i in {1..50000}; do dd if=/dev/urandom bs=4096 count=1 of=file$i; done
And with the dd command we saw that the same thing happened ( the kernel memory grew until OOM).
After k8s restarted the pod, I got doing a describe pod:
Last State:Terminated
Reason: OOMKilled
Exit Code: 143
Creating files cause the kernel memory grows, deleting those files cause the memory decreases . But our services store data , so it creates a lot of files continuously, until the pod is killed and restarted because OOMKilled.
We tested limiting the kernel memory using a stand alone docker with the --kernel-memory parameter and it worked as expected. The kernel memory grew to the limit and did not rise anymore. But we did not find any way to do that in a kubernetes cluster.
Is there a way to limit the kernel memory in a K8S environment ?
Why the creation of files causes the kernel memory grows and it is not released ?

Answer 1

Thanks for all this info, it was very useful!
On my app, I solved this by creating a new side container that runs a cron job, every 5 minutes with the following command:
echo 3 > /proc/sys/vm/drop_caches
(note that you need the side container to run in privileged mode)
It works nicely and has the advantage of being predictable: every 5 minutes, your memory cache will be cleared.