Date:   Fri, 14 Jan 2022 11:18:45 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Xiongwei Song <sxwjean@gmail.com>
Cc:     Xiongwei Song <sxwjean@me.com>, akpm@linux-foundation.org,
        David Hildenbrand <david@redhat.com>, dan.j.williams@intel.com,
        osalvador@suse.de, naoya.horiguchi@nec.com,
        thunder.leizhen@huawei.com, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 2/2] proc: Add getting pages info of ZONE_DEVICE
 support
Message-ID: <YeFOBWz1OZTpEuwt@dhcp22.suse.cz>
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 <CAEVVKH-L-6Yra75XEWUNiq=ajJmtWauDTcmN=b1VCcJ0NVS7OA@mail.gmail.com>
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On Fri 14-01-22 18:03:04, Xiongwei Song wrote:
> HI Michal,
> 
> On Thu, Jan 13, 2022 at 11:31 PM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Wed 12-01-22 22:35:17, sxwjean@me.com wrote:
> > > From: Xiongwei Song <sxwjean@gmail.com>
> > >
> > > When requesting pages info by /proc/kpage*, the pages in ZONE_DEVICE were
> > > ignored.
> > >
> > > The pfn_to_devmap_page() function can help to get page that belongs to
> > > ZONE_DEVICE.
> >
> > Why is this needed? Who would consume that information and what for?
> 
> It's for debug purpose, which checks page flags in system wide. No any other
> special thought. But it looks like it's not appropriate to expose now from my
> understand, which is from David's comment.
> https://lore.kernel.org/linux-mm/20220110141957.259022-1-sxwjean@me.com/T/#m4eccbb2698dbebc80ec00be47382b34b0f64b4fc

yes, I do agree with David. This is the reason I am asking because I do
remember we have deliberately excluded those pages. If there is no real
user to use that information then I do not think we want to make the
code more complex and check for memmap and other peculiarities.

Thanks!
-- 
Michal Hocko
SUSE Labs