Re: [PATCH v2] docs: cgroup: document empty-write behavior of memory limit knobs

[Shakeel Butt]

On Wed, Aug 26, 2026 at 10:17:53AM +0800, Tao Cui wrote:
> From: Tao Cui <cuitao@xxxxxxxxxx>
> 
> A maintenance script on a cluster wrote an unset variable into
> memory.max of a workload cgroup; the variable expanded to an empty
> string, the write succeeded, and the workload in the cgroup was
> OOM-killed.  Nothing pointed back at the write, so it took quite
> some time to trace the OOM kills to that script.
> 
> The memory controller documentation does not say what an empty
> write does; the cpuset controller documents its empty-value
> semantics.  The actual behavior is that the empty string is
> accepted as 0.  Reproduced on a k8s cluster (v1.29, cgroup v2,
> two-container pod, 384M limit):
> 
>   # LIMIT=
>   # echo "$LIMIT" > $CG/memory.max
>   # echo $?
>   0
> 
>   m6demo   0/2     OOMKilled   0
> 
>   Memory cgroup out of memory: Killed process 339529 (sleep) ... anon-rss:32kB
> 
> State it where the interface files are introduced, alongside the
> existing notes on units and page rounding.
> 
> Link: https://lore.kernel.org/all/aoVUlFdZYLFn_gvJ@tiehlicka/
> Signed-off-by: Tao Cui <cuitao@xxxxxxxxxx>

Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>