Re: [RFC PATCH] mm: z3fold: rename CONFIG_Z3FOLD to CONFIG_Z3FOLD_DEPRECATED

[Yosry Ahmed <yosryahmed@google.com>]

On Sun, Jan 14, 2024 at 2:42 PM Nhat Pham <nphamcs@gmail.com> wrote:
>
> On Sun, Jan 14, 2024 at 10:49 AM Yosry Ahmed <yosryahmed@google.com> wrote:
> >
> > On Fri, Jan 12, 2024 at 4:38 PM Nhat Pham <nphamcs@gmail.com> wrote:
> > >
> > > On Fri, Jan 12, 2024 at 3:37 PM Yosry Ahmed <yosryahmed@google.com> wrote:
> > > >
> > > > On Fri, Jan 12, 2024 at 11:42 AM Nhat Pham <nphamcs@gmail.com> wrote:
> > > > >
> > > > > On Fri, Jan 12, 2024 at 11:31 AM Yosry Ahmed <yosryahmed@google.com> wrote:
> > > > > >
> > > > > > The z3fold compressed pages allocator is not widely used, most users use
> > > > > > zsmalloc. The only disadvantage of zsmalloc in comparison is the
> > > > > > dependency on MMU, and zbud is a more common option for !MMU as it was
> > > > > > the default zswap allocator for a long time.
> > > > >
> > > > > Johannes and I were chatting about this the other day. We might be
> > > > > able to disable certain zsmalloc behavior in the case of !MMU, making
> > > > > it available there too. Once that's happened, we can outright remove
> > > > > z3fold and zbud, and have one allocator to rule them all? :)
> > > >
> > > > (Adding Sergey and Minchan for visibility)
> > > >
> > > > I didn't want to bring up the zsmalloc MMU dependency in this thread
> > > > to reduce noise, but that's also what I had in mind. Sergey and I were
> > > > also chatting about this the other day :)
> > > >
> > > > I thought deprecating z3fold is the low hanging fruit. Then, once we
> > > > can sort out the MMU dependency in zsmalloc, we can go after zbud as
> > > > well.
> > >
> > > Makes sense to me. Should we do the same thing to zbud? We probably
> > > have even less of a case for it, no?
> >
> > Do you mean declare it as deprecated now? I initially thought that
> > would only be appropriate to do after zsmalloc has no dependency on
> > MMU, so that we can confidently say zbud has no practical use case.
>
> Ah, I misread your email. My bad. Personally, I'd like to declare both
> (zbud and z3fold) as deprecated. That said, no strong feelings here -
> as long as (eventually) we move towards retiring both of them. So my
> original ACK still holds.
>
> Not entirely sure which should we remove first between zbud and z3fold
> though. I was under the assumption that z3fold is slightly better, but
> that could be my bias for shiny new things showing :)

My rationale is that zbud was the default zswap allocator for a long
time, so it's the one we should keep for now as it is more likely to
have users. That said, I don't know of any users of either zbud or
z3fold, and I am fine starting with deprecating either.