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

[Yosry Ahmed]

> > > Youngjun is working on swap tiers. At the moment he is more interested in
> > > allowing a specific swap device to a memcg or not. I can imagine in future there
> > > will be use-cases where there will be a need to demote data on higher tier swap
> > > to lower tier swap. What would be the appropriate interface?
> > >
> > > BTW does zswap folks think of zswap as a top swap tier or something different?
> >
> > I haven't been following the swap tiers work closely, but personally I
> > do think of zswap as a top swap tier.
>
> Same for me though I imagine swap tiers would introduce some duplication i.e.
> different way (interface) to set limits for swap tiers for a given memcg.
>
> > Things will probably get more
> > blurry with memory tiers and compressed memory nodes though.
>
> I think there will still be distinction between byte addressable and fault on
> access devices.

Yeah, I think it makes sense to define "swap" as fault on access
(zswap, SSD, etc), and memory tiers as byte-addressable (even if you
put an SSD behind CXL and make it byte-addressable). But I also
remember seeing discussions about unifying memory tiers and swap in a
way, and it makes sense from a reclaim perspective (swap or demote
first?).