Re: [PATCH 4/5] mm: zswap: add basic meminfo and vmstat coverage

Yu Zhao
2022-05-05T23:54:02Z

On Thu, May 5, 2022 at 3:25 PM Suleiman Souhlal <suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> wrote:
>
> On Fri, May 6, 2022 at 4:33 AM Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> wrote:
> >
> > On Thu, Apr 28, 2022 at 9:54 AM Yang Shi <shy828301-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > >
> > [...]
> > > > Yes, we have some modifications to zswap to make it work without any
> > > > backing real swap. Though there is a future plan to move to zram
> > > > eventually.
> > >
> > > Interesting, if so why not just simply use zram?
> > >
> >
> > Historical reasons. When we started trying out the zswap, I think zram
> > was still in staging or not stable enough (Suleiman can give a better
> > answer).
>
> One of the reasons we chose zswap instead of zram is that zswap can
> reject pages.
> Also, we wanted to have per-memcg pools, which zswap made much easier to do.

Yes, it was a design choice. zswap was cache-like (tiering) and zram
was storage-like (endpoint). Though nowadays the distinction is
blurry.

It had nothing to do with zram being in staging -- when we took zswap,
it was out of the tree.