Re: [PATCH v9 0/6] mm/swap, memcg: Introduce swap tiers for cgroup based swap control

[Yosry Ahmed]

On Sat, Jun 20, 2026 at 11:16 AM Youngjun Park <her0gyugyu@xxxxxxxxx> wrote:
>
> This is the v9 series of the swap tier patchset.
>
> The main change in this version is the addition of selftests for the tier
> interfaces, requested by Nhat; see the changelog below for the other changes.
> I designed the test cases and wrote the selftests with some AI assistance.
>
> For context, the bulk of the series is unchanged since v8, with great thanks
> to Shakeel Butt and Yosry for the reviews and discussions [1] that shaped it.
> The main change in v8 was the interface change to use memory.swap.tiers.max
> with '0' (disable) and 'max' (enable) values. This mechanism was suggested
> by Shakeel and Yosry.
>
> This change allows for future extensions to control swap between tiers and
> aligns better with existing memcg interfaces. It is confined to patch #3's
> user-facing interface; internally, patch #3 still uses the existing mask
> processing method, which is implementation-efficient.
>
> We also discussed tier extensions. Thanks to Yosry, Nhat and Shakeel for their
> valuable feedback.
>
> Here is a brief summary of our tentative conclusions. Please correct me
> if anything is misrepresented (details in references):
>
> * Zswap tiering [2]:
>   Tiering applies only to the vswap + zswap combo. Zswap itself will
>   not be tiered, as the current architecture requires a physical device
>   for zswap allocation.

I thought we agreed that zswap should be a tier, so that proactive
zswap writeback can be implemented as proactive swap demotion?

The only restriction we talked about is that zswap cannot be the only
allowed tier as long as vswap isn't supported. We can lift the
restriction when vswap support is added.