linux-kernel - Re: [RFC PATCH v2] mm: initialize struct pages reserved by ZONE

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Message-ID: <CAPcyv4jkZJLzEDne6W2pEDGB+q96NkkozmhKxybTu1LjnPYY9g@mail.gmail.com>
Date:   Tue, 10 Sep 2019 07:53:17 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Toshiki Fukasawa <t-fukasawa@...jp.nec.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "adobriyan@...il.com" <adobriyan@...il.com>,
        "hch@....de" <hch@....de>,
        "longman@...hat.com" <longman@...hat.com>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "mst@...hat.com" <mst@...hat.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Junichi Nomura <j-nomura@...jp.nec.com>
Subject: Re: [RFC PATCH v2] mm: initialize struct pages reserved by
 ZONE_DEVICE driver.

On Tue, Sep 10, 2019 at 7:01 AM Michal Hocko <mhocko@...nel.org> wrote:
>
> On Fri 06-09-19 08:09:52, Toshiki Fukasawa wrote:
> [...]
> > @@ -5856,8 +5855,6 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> >               if (!altmap)
> >                       return;
> >
> > -             if (start_pfn == altmap->base_pfn)
> > -                     start_pfn += altmap->reserve;
> >               end_pfn = altmap->base_pfn + vmem_altmap_offset(altmap);
>
> Who is actually setting reserve? This is is something really impossible
> to grep for in the kernle and git grep on altmap->reserve doesn't show
> anything AFAICS.

Yes, it's difficult to grep, here is the use in the nvdimm case:

    https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/nvdimm/pfn_devs.c#n600

>
> Btw. irrespective to this issue all three callers should be using
> pfn_to_online_page rather than pfn_to_page AFAICS. It doesn't really
> make sense to collect data for offline pfn ranges. They might be
> uninitialized even without zone device.

Agree.