Re: [TECH TOPIC] Per-cgroup Swap Device Control

[Matthew Wilcox <willy@infradead.org>]

On Fri, Aug 22, 2025 at 05:14:51PM +0900, YoungJun Park wrote:
> Abstract:
> Enabling cgroup-level control over swap devices for diverse workloads
> 
> Proposal:
> I am developing on a restricted internal platform where there is a
> technical requirement to use idle devices as extended memory.

I don't think this is appropriate for the maintainer summit.  You
can submit it to the Plumbers MM microconf [1] or LSFMM in May.

[1] https://lpc.events/event/19/contributions/1995/

Also you should have cc'd linux-mm for this kind of thing, adding
it now.  Preserving the rest of the proposal for those who are
interested.

> One motivating scenario discussed was to configure background processes
> to use slow swap (network) while foreground processes use fast swap
> (local storage).
> 
> Currently, the kernel does not provide per-process or per-cgroup swap
> selection, making this idea unachievable. To meet this usage need, and
> after reviewing alternatives, I reached the conclusion that swap
> devices must be controllable on a per-cgroup basis.
> 
> I would like to present the motivation, implementation progress, and
> directions of this work, and invite discussion and feedback from the
> community. Through prior exchanges with Chris Li[1], I also recognized
> that this topic has already triggered meaningful technical debate, and
> I believe a broader discussion at Kernel Summit would be valuable.
> 
> Agenda:
> 1. Motivation for per-cgroup swap priority [2]
>    - Comparison with alternative approaches
> 
> 2. Implementation reviews and problem solving
>    - Changes in percpu clusters & swap [3]
>    - Consistency with cgroup parent-child semantics [4]
>    - Challenges with NUMA autobind and swap priority [5]
> 
> 3. Criticism and alternative ideas
>    - Technical concerns raised by Chris Li [6]
>    - Introduction of the swap tier approach
> 
> 4. Further discussion
>    - Topics expected to arise in ongoing reviews before Plumbers
> 
> These agenda items reflect issues that have emerged through the ongoing
> RFC → PATCH development process. The presentation aims to summarize
> these discussions, share the current direction, and invite further
> feedback and open discussion from the community.
> 
> [1] https://lore.kernel.org/linux-mm/CAF8kJuMo3yNKOZL9n5UkHx_O5cTZts287HOnQOu=KqQcnbrMdg@mail.gmail.com/
> [2] https://lore.kernel.org/linux-mm/20250612103743.3385842-1-youngjun.park@lge.com/
> [3] https://lore.kernel.org/linux-mm/CAMgjq7BJE9ALFG4N8wb-hdkC+b-8d1+ckXL9D6pbbfgiXfuzPA@mail.gmail.com/
> [4] https://lore.kernel.org/linux-mm/rivwhhhkuqy7p4r6mmuhpheaj3c7vcw4w4kavp42avpz7es5vp@hbnvrmgzb5tr/
> [5] https://lore.kernel.org/linux-mm/jrkh2jy2pkoxgsxgsstpmijyhbzzyige6ubltvmvwl6fwkp3s7@kzc24pj2tcko/
> [6] https://lore.kernel.org/linux-mm/CAF8kJuMo3yNKOZL9n5UkHx_O5cTZts287HOnQOu=KqQcnbrMdg@mail.gmail.com/