Re: [swap tier discussion] Re: [PATCH v3 2/4] mm/zswap: Implement proactive writeback

[Yosry Ahmed]

On Tue, Jun 16, 2026 at 1:09 PM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
>
> On Tue, Jun 16, 2026 at 3:54 PM Yosry Ahmed <yosry@xxxxxxxxxx> wrote:
> >
> > On Tue, Jun 16, 2026 at 11:33 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
> > >
> > > TBH, without vswap, we should not allow setting zswap as its own tier.
> > > It's meaningless. Maybe makes it a no-op, and warn users what they're
> > > setting is gibberish?
> >
> > Why? vswap is transparent to the user. Why can't zswap be its own tier?
>
> Without vswap, if you set zswap as its own tier, which phys swap
> device should we allocate from for the backing slot? :)

Today we just allocate a swap slot in a swapfile during reclaim,
before swapout, and zswap will just writeback to that one. I assume
the same will work with swap tiering, except that maybe the way that
swap slot will respect the allowed swap tiers?

>
> With vswap then it makes sense (and would probably be the "default"
> for zswap setup until we enable zswap writeback).