linux-kernel - Re: [PATCH 1/5] mm: introduce PAGEFLAGS_MASK to replace ((1UL << NR_PAGEFLAGS)

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Message-ID: <CAMZfGtUtk9uyO7v0v94YqLaHhrZ-CoFvVH60n54apib7PHPcKw@mail.gmail.com>
Date:   Tue, 27 Jul 2021 14:27:31 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
        David Hildenbrand <david@...hat.com>,
        Chen Huang <chenhuang5@...wei.com>,
        "Bodeddula, Balasubramaniam" <bodeddub@...zon.com>,
        Jonathan Corbet <corbet@....net>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        fam.zheng@...edance.com, linux-doc@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH 1/5] mm: introduce PAGEFLAGS_MASK to replace ((1UL <<
 NR_PAGEFLAGS) - 1)

On Tue, Jul 27, 2021 at 5:04 AM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>
> On 7/14/21 2:17 AM, Muchun Song wrote:
> > Instead of hard-coding ((1UL << NR_PAGEFLAGS) - 1) everywhere, introducing
> > PAGEFLAGS_MASK to make the code clear to get the page flags.
> >
> > Signed-off-by: Muchun Song <songmuchun@...edance.com>
> > ---
> >  include/linux/page-flags.h      | 4 +++-
> >  include/trace/events/page_ref.h | 4 ++--
> >  lib/test_printf.c               | 2 +-
> >  lib/vsprintf.c                  | 2 +-
> >  4 files changed, 7 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> > index 5922031ffab6..358d3f6fa976 100644
> > --- a/include/linux/page-flags.h
> > +++ b/include/linux/page-flags.h
> > @@ -178,6 +178,8 @@ enum pageflags {
> >       PG_reported = PG_uptodate,
> >  };
> >
> > +#define PAGEFLAGS_MASK               (~((1UL << NR_PAGEFLAGS) - 1))
>
> Can you explain why you chose this definition instead of
>
> #define PAGEFLAGS_MASK          ((1UL << NR_PAGEFLAGS) - 1)
>
> and mostly use ~PAGEFLAGS_MASK below?

Hi Mike,

Actually, I learned from PAGE_MASK. So I thought the macro
like xxx_MASK should be the format of 0x00...00ff...ff. I don't
know if this is an unwritten rule. Please correct me if I am
wrong.

Thanks.

> --
> Mike Kravetz