Re: [PATCH] cgroup/dmem: implement dmem.high soft limit and throttling

[Qiliang Yuan]

Hello Tejun,

On Wed, May 20, 2026 at 09:52 AM Tejun Heo wrote:
> I'm not sure about complicating dmem control model without implementing
> reclaim. What are we slowing them down for if the only recovery action is
> killing them?

Thank you for the feedback. Your point about the lack of a reclaim path 
is well-taken. Simple throttling without a way to recover resources is 
indeed incomplete and inconsistent with the cgroup v2 philosophy.

To address this from several perspectives in v2:

1. Recovery Path: As suggested by Maarten Lankhorst, we will pivot to a 
reclaim-centric model. Exceeding `dmem.high` will trigger a prioritized 
eviction process, where memory objects from over-limit cgroups are 
targeted first for reclaim. This provides the meaningful "recovery action" 
you mentioned.

2. Backpressure: Throttling will then serve as a secondary tool to 
synchronize user-space demand with the kernel's reclaim speed, preventing 
bursty workloads from overwhelming the system before reclaim can finish.

3. Graceful Degradation: For GPU compute jobs, this model provides a 
managed "pressure point" that allows transient peaks to be handled via 
rebalancing rather than immediate, fatal allocation failures (max/OOM).

The goal for v2 is to achieve convergence with the `memory.high` model, 
pairing prioritized reclaim with backpressure.

Thanks,
Qiliang