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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Thu, 29 Jul 2021 14:00:28 +0800
Message-ID: <CAMZfGtXmNSg2mNsdG20JDzZofMSdreYOiKCO1WQ+zAEomkozyw@mail.gmail.com>
Subject: Re: [PATCH 1/5] mm: introduce PAGEFLAGS_MASK to replace ((1UL <<
 NR_PAGEFLAGS) - 1)
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>,
        "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
        David Hildenbrand <david@redhat.com>,
        Chen Huang <chenhuang5@huawei.com>,
        "Bodeddula, Balasubramaniam" <bodeddub@amazon.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Xiongchun duan <duanxiongchun@bytedance.com>,
        fam.zheng@bytedance.com, linux-doc@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Qi Zheng <zhengqi.arch@bytedance.com>
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On Tue, Jul 27, 2021 at 2:27 PM Muchun Song <songmuchun@bytedance.com> wrote:
>
> On Tue, Jul 27, 2021 at 5:04 AM Mike Kravetz <mike.kravetz@oracle.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@bytedance.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
                                           ^^^
Sorry. I mean 0xff...ff00...00 here.

> know if this is an unwritten rule. Please correct me if I am
> wrong.
>
> Thanks.
>
> > --
> > Mike Kravetz