Possible memory leak in 6.17.7

Mal Haak
2025-11-10T08:24:52Z

Hello,

I have found a memory leak in 6.17.7 but I am unsure how to track it
down effectively.

I am running a server that has a heavy read/write workload to a cephfs
file system. It is a VM.

Over time it appears that the non-cache useage of kernel dynamic memory
increases. The kernel seems to think the pages are reclaimable however
nothing appears to trigger the reclaim. This leads to workloads getting
killed via oomkiller.

smem -wp output:

Area Used Cache Noncache
firmware/hardware 0.00% 0.00% 0.00%
kernel image 0.00% 0.00% 0.00%
kernel dynamic memory 88.21% 36.25% 51.96%
userspace memory 9.49% 0.15% 9.34%
free memory 2.30% 2.30% 0.00%

free -h output:

total used free shared buff/cache available
Mem: 31Gi 3.6Gi 500Mi 4.0Mi 11Gi 27Gi
Swap: 4.0Gi 179Mi 3.8Gi

Reverting to the previous LTS fixes the issue

smem -wp output:
Area Used Cache Noncache
firmware/hardware 0.00% 0.00% 0.00%
kernel image 0.00% 0.00% 0.00%
kernel dynamic memory 80.22% 79.32% 0.90%
userspace memory 10.48% 0.20% 10.28%
free memory 9.30% 9.30% 0.00%

I am unsure of the best way to track down the memory usage. I have
tried stopping the workload and unmounting the cephfs filesystem. As
well as removing the ceph and network related kernel modules.

I assume some kind of tracing would be a way to find the culprit,
however I am unsure of the best way to do that.

I can do a git bisect and am in the process of getting a test
reproducer made for that.

But if there is an easier way to do it I would happily do that.

Just to note, slabtop looks normal and doesn't show the memory usage.

Thanks in advance

Mal