linux-kernel - Re: [PATCH] mm/damon/vaddr: remove unnecessary switch case DAMOS

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Message-ID: <CAGjdHukJ+HVxZo66oVGnETy6Zm+LMDyVS6upEzQ14ucpj8NvXA@mail.gmail.com>
Date:   Thu, 8 Sep 2022 10:07:39 +0800
From:   Kaixu Xia <xiakaixu1987@...il.com>
To:     SeongJae Park <sj@...nel.org>
Cc:     akpm@...ux-foundation.org, damon@...ts.linux.dev,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        Kaixu Xia <kaixuxia@...cent.com>
Subject: Re: [PATCH] mm/damon/vaddr: remove unnecessary switch case DAMOS_STAT

Hi SJ,

On Thu, Sep 8, 2022 at 1:42 AM SeongJae Park <sj@...nel.org> wrote:
>
> Hi Kaixu,
>
> On Thu, 8 Sep 2022 00:31:02 +0800 xiakaixu1987@...il.com wrote:
>
> > From: Kaixu Xia <kaixuxia@...cent.com>
> >
> > The switch case DAMOS_STAT and switch case default have same
> > return value in damon_va_apply_scheme(), so we can combine them.
>
> Good point.  I have a comment below, though.
>
> >
> > Signed-off-by: Kaixu Xia <kaixuxia@...cent.com>
> > ---
> >  mm/damon/vaddr.c | 2 --
> >  1 file changed, 2 deletions(-)
> >
> > diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> > index 3c7b9d6dca95..94ae8816a912 100644
> > --- a/mm/damon/vaddr.c
> > +++ b/mm/damon/vaddr.c
> > @@ -643,8 +643,6 @@ static unsigned long damon_va_apply_scheme(struct damon_ctx *ctx,
> >       case DAMOS_NOHUGEPAGE:
> >               madv_action = MADV_NOHUGEPAGE;
> >               break;
> > -     case DAMOS_STAT:
> > -             return 0;
>
> IMHO, keeping the 'case' makes the code easier to read, as we can find what is
> the expected flow for DAMOS_STAT here immediately, instead of asking readers to
> find what are the actions that not specified here and therefore fall though to
> 'default'.
>
> Also, my another intention here is to mark 'DAMOS_STAT' is supported by
> 'vaddr'.
>
> >       default:
> >               return 0;
>
> That is, 'default' case here is for DAMOS actions that not supported by
> 'vaddr'.  So, I'd like to keep the code as is.  Maybe we could add a comment
> saying 'default' case is for DAMOS actions that not yet supported by 'vaddr'.
>
Yeah,  it might make sense to add a comment here, thanks.
> >       }
> > --
> > 2.27.0
>
>
> Thanks,
> SJ