Re: [LSF/MM/BPF TOPIC] Reimagining Memory Cgroup (memcg_ext)

[Jiayuan Chen <jiayuan.chen@linux.dev>]

On 3/8/26 2:24 AM, Shakeel Butt wrote:
> Over the last couple of weeks, I have been brainstorming on how I would go
> about redesigning memcg, taking inspiration from sched_ext and bpfoom, with a
> focus on existing challenges and issues. This proposal outlines the high-level
> direction. Followup emails and patch series will cover and brainstorm the
> mechanisms (of course BPF) to achieve these goals.
>
> Memory cgroups provide memory accounting and the ability to control memory usage
> of workloads through two categories of limits. Throttling limits (memory.max and
> memory.high) cap memory consumption. Protection limits (memory.min and
> memory.low) shield a workload's memory from reclaim under external memory
> pressure.
>
> Challenges
> ----------
>
> - Workload owners rarely know their actual memory requirements, leading to
>    overprovisioned limits, lower utilization, and higher infrastructure costs.
>
> - Throttling limit enforcement is synchronous in the allocating task's context,
>    which can stall latency-sensitive threads.
>
> - The stalled thread may hold shared locks, causing priority inversion -- all
>    waiters are blocked regardless of their priority.
>
> - Enforcement is indiscriminate -- there is no way to distinguish a
>    performance-critical or latency-critical allocator from a latency-tolerant
>    one.
>
> - Protection limits assume static working sets size, forcing owners to either
>    overprovision or build complex userspace infrastructure to dynamically adjust
>    them.
>
> Feature Wishlist
> ----------------
>
> Here is the list of features and capabilities I want to enable in the
> redesigned memcg limit enforcement world.
>
> Per-Memcg Background Reclaim
>
> In the new memcg world, with the goal of (mostly) eliminating direct synchronous
> reclaim for limit enforcement, provide per-memcg background reclaimers which can
> scale across CPUs with the allocation rate.

This sounds like a very useful approach. I have a few questions I'm 
thinking through:

How would you approach implementing this background reclaim? I'm imagining
something like asynchronous memory.reclaim operations - is that in line
with your thinking?

And regarding cold page identification - do you have a preferred approach?
I'm curious what the most practical way would be to accurately identify
which pages to reclaim.

Would be great to hear your perspective.