Re: Possible memory leak in 6.17.7

[David Wang]

On Mon, 10 Nov 2025 18:20:08 +1000
Mal Haak <malcolm@xxxxxxxxxx> wrote:
> 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 think the `memory allocation profiling` feature can help.
https://docs.kernel.org/mm/allocation-profiling.html

You would need to build a kernel with 
CONFIG_MEM_ALLOC_PROFILING=y
CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=y

And check /proc/allocinfo for the suspicious allocations which take
more memory than expected.

(I once caught a nvidia driver memory leak.)


FYI
David