Re: [RFC PATCH v2] mm: initialize struct pages reserved by ZONE_DEVICE driver.

From: Michal Hocko <mhocko@kernel.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Toshiki Fukasawa <t-fukasawa@vx.jp.nec.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"adobriyan@gmail.com" <adobriyan@gmail.com>,
	"hch@lst.de" <hch@lst.de>,
	"longman@redhat.com" <longman@redhat.com>,
	"sfr@canb.auug.org.au" <sfr@canb.auug.org.au>,
	"mst@redhat.com" <mst@redhat.com>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	Junichi Nomura <j-nomura@ce.jp.nec.com>
Subject: Re: [RFC PATCH v2] mm: initialize struct pages reserved by ZONE_DEVICE driver.
Date: Tue, 10 Sep 2019 19:35:37 +0200	[thread overview]
Message-ID: <20190910173537.GB4023@dhcp22.suse.cz> (raw)
In-Reply-To: <CAPcyv4jkZJLzEDne6W2pEDGB+q96NkkozmhKxybTu1LjnPYY9g@mail.gmail.com>

On Tue 10-09-19 07:53:17, Dan Williams wrote:
> On Tue, Sep 10, 2019 at 7:01 AM Michal Hocko <mhocko@kernel.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

Thanks! I am still not sure what the proper fix is but this is a useful
pointer.

-- 
Michal Hocko
SUSE Labs