Re: [PATCH v10 0/6] mm/swap, memcg: Introduce swap tiers for cgroup based swap control

[Chris Li]

On Mon, Jul 13, 2026 at 9:01 AM Yosry Ahmed <yosry@xxxxxxxxxx> wrote:
> > My plan is to land the swap tier infrastructure together with the
> > first use case (cgroup-based swap control) first, and then follow
> > up with zswap tier support in a subsequent series, continuing the
> > discussions we've had above.
> > (I mentioned on cover letter, right above the overview section)
> >
> > Does that approach sound reasonable to you?
>
> How does swap tiering work with zswap in the current series? I assume
> zswap is just enabled for all devices in all tiers? I wonder if

Zswap is not part of the tiers exactly because it sits in front of all
swap devices (tiers) and uses a different control to enable or disable
it.
Let's not combine these two; let zswap use its own existing cgroup
control interface.

> introducing zswap as a tier after the fact changes user-visible
> behavior. I guess if zswap will be introduced with a default "max"
> value it will more-or-less be the same behavior, but I would check all
> user-visible behaviors related to zswap (e.g. interaction with other
> zswap interfaces) to make sure nothing breaks or changes in a
> meaningful way when zswap is introduced as a tier later.

Zswap will not be introduced as a tier. The existing user interface
makes zswap not exactly compatible with the tier ordering because it
sits in front of every swapfile. If we change that, we break the user
interface. I suggest we keep zswap working as it is now.

Chris