Re: Path forward for Virtualized Swap?

[Gregory Price (Meta)]

On 2026-10-23 13:25 -0700, Yosry Ahmed wrote:
> On Fri, Oct 23, 2026 at 1:03 PM Rik van Riel <riel@xxxxxxxxxxx> wrote:
> >
> > +-------+     +------------+
> > | vswap |-----| swap cache |
> > +---+---+     +------------+
> >     |
> >     +----------+-----------+
> >     |          |           |
> > +---+---+  +---+---+   +---+---+
> > | swap  |  | zswap |   | zram  |
> > | file  |  |       |   |       |
> > +-------+  +-------+   +-------+
> >
> > What exactly do people want to accomplish here?
> 
> Today if you swapoff a swapfile, every is swapped in into the
> swapcache, whether it's in zswap or on disk. With vswap, you have no
> way to trigger swapin of compressed memory in zswap.
> 

This seems like a missing interface in zswap, rather than something
vswap needs.  But you could just write this as

vswap swapoff {
  disable new backend writeback (swapcache fault-in only)

  for each backend {
    backend swapoff
  }
}

so rather than vswap.swapoff() you'd actually just want a stop-bit that
says to disable the swap subsystem writeback behavior to all backends.

Otherwise the user can just disable each backend individually.

-- 
~Gregory