Re: [PATCH v6 0/6] [PATCH v6 0/6] Add reclaim to the dmem cgroup controller

[Tejun Heo <tj@kernel.org>]

On Mon, Jun 15, 2026 at 08:49:55AM -1000, Tejun Heo wrote:
> The canonical behavior for cgroup2 would be not failing the write at all
> even when the usage can't be brought down below the new max. Updating the
> target configuration and tracking the current usage are separate operations.
> The former should just set max and trigger reclaim and a writer should not
> assume that a successful write indicates that the usage is below the written
> max value.

Sent too early. One of the reasons is that cgroup is hierarchical and there
can be multiple delegation layers and if you tie application of configuration
to immediate enforcement, some hierarchical control actions become racy and
awkward.

Here's an example: Imagine a system agent trying to lower usage in a subtree
which contains multiple delegated containers. If max can be set below what
reclaim can achieve immediately, it can just set the max and if the usage is
still too high, can go around and e.g. kill some of the containers. If max
write fails, it'd have to kill and then try again and inbetween someone else
might push up the usage.

Thanks.

-- 
tejun