Re: [RFC PATCH v2 3/7] mm, swap: support physical swap as a vswap backend

[Nhat Pham]

On Mon, Jun 22, 2026 at 5:23 PM Yosry Ahmed <yosry@xxxxxxxxxx> wrote:
>
> On Fri, Jun 12, 2026 at 12:37:34PM -0700, Nhat Pham wrote:
> > Add physical swap as a backend for the virtual swap layer.
> >
> > With physical swap backing, vswap can allocate a physical slot on
> > demand when needed: as a fallback for zswap_store failures, or as
> > the destination for zswap writeback.
> >
> > Each vswap entry's physical slot is tracked via a Pointer-tagged
> > swap_table entry on the physical cluster (rmap back to the vswap
> > entry).
> >
> > Suggested-by: Kairui Song <kasong@xxxxxxxxxxx>
> > Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
>
> I didn't look through the rest of the series, but are there use cases
> for calling folio_realloc_swap() without calling vswap_zswap_load()
> first? I wonder if the realloc_swap API should take the swpentry
> directly and do the load within? Something like
> vswap_alloc_phys(swpentry, folio)?

It's also use on the swapout fallback path! If zswap rejects the page
or is disabled, and memory.zswap.writeback=1, then we allocate phys
swap space. We probably don't wanna do zswap_load() there again :)