Re: [RFC PATCH 0/7] mm: store zswap entries in swap table (Pointer entry)

[Yosry Ahmed]

On Tue, Jul 7, 2026 at 12:28 PM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
>
> On Tue, Jul 7, 2026 at 12:32 AM Baoquan He <baoquan.he@xxxxxxxxx> wrote:
> >
> > Currently zswap uses a per-swap-device xarray to map swap offsets to
> > zswap_entry pointers. This introduces an additional tree walk on every
> > zswap entry access.
> >
> > This series replaces the xarray with a "Pointer" entry type stored
> > directly in the swap cluster table. The new swp_tb_t variant embeds
> > a zswap_entry pointer plus a entry count, eliminating the xarray and
> > its lookup overhead entirely.
> >
>
> Have you had the chance to review the virtual swap work (latest
> version in [1])? At a first glance, it bears a lot of similarity to
> this.
>
> We're envisioning this to be the future architecture for zswap :) Is
> there anything that is missing that would satisfy your use case too?
>
> [1]: https://lore.kernel.org/all/20260612193738.2183968-1-nphamcs@xxxxxxxxx/

Yeah this doubles down on the dependency of zswap on a swapfile being
present, but I guess the goal is for this to be complimented by your
other series to add ghost swapfile support. This was discussed at
length, and we don't really want to have a user-facing ghost/virtual
swapfile concept, at least not for now. Nhat's latest proposal is
essentially a ghost/virtual swapfile implementation that is
transparent to userspace, AFAICT.

As Nhat mentioned, if there are deficiencies in his proposal that are
addressed by yours, I think the most productive way forward is to
start a discussion (here or on Nhat's proposal) to figure out the best
way forward for everyone.