linux-kernel - Re: [PATCH 2/2] zsmalloc: fine-grained inuse ratio based fullness grouping

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Message-ID: <CAJD7tka3s84v9-ZA-OZkBkina6MByCSFnKXwv+hq8o8nZSZoyg@mail.gmail.com>
Date:   Thu, 9 Feb 2023 20:25:46 -0800
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 2/2] zsmalloc: fine-grained inuse ratio based fullness grouping

On Thu, Feb 9, 2023 at 8:24 PM Sergey Senozhatsky
<senozhatsky@...omium.org> wrote:
>
> On (23/02/07 10:47), Sergey Senozhatsky wrote:
> > > >  enum fullness_group {
> > > > -       ZS_EMPTY,
> > > > -       ZS_ALMOST_EMPTY,
> > > > -       ZS_ALMOST_FULL,
> > > > -       ZS_FULL,
> > > > +       ZS_USAGE_0,
> > > > +       ZS_USAGE_10,
> > > > +       ZS_USAGE_20,
> > > > +       ZS_USAGE_30,
> > > > +       ZS_USAGE_40,
> > > > +       ZS_USAGE_50,
> > > > +       ZS_USAGE_60,
> > > > +       ZS_USAGE_70,
> > > > +       ZS_USAGE_80,
> > > > +       ZS_USAGE_90,
> > > > +       ZS_USAGE_99,
> > > > +       ZS_USAGE_100,
> > > >         NR_ZS_FULLNESS,
> > > >  };
> > > >
> > >
> > > Is there a reason why this can't be done with something like #define
> > > FULLNESS_GROUPS 10? We can make sure during build that (100 %
> > > FULLNESS_GROUPS == 0) to make our lives easier. I feel like the code
> > > will be much more concise and easier to navigate, instead of multiple
> > > enums and static arrays.
> >
> > I wanted to keep things the way they are to make reviews simpler.
> > We probably can do something more "disruptive" in a separate patch.
>
> Forgot to mention, I was also thinking about extending zsmalloc stats
> file and providing values for each fullness group per class, as opposed
> to current ALMOST_EMPTY and ALMOST_FULL stats, which don't tell much.

Makes sense.

>
> I can get rid of static const arrays and pass "begin / end" group IDs to
> functions that iterate fullness lists and pick the first head page, but
> I think that enum values will stay.

Do they have to stay for a technical reason or just to make reviews simpler?