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Date: Thu, 15 Jul 2021 13:59:05 +0100
From: Christoph Hellwig <hch@infradead.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Joao Martins <joao.m.martins@oracle.com>, Linux MM <linux-mm@kvack.org>,
	Vishal Verma <vishal.l.verma@intel.com>,
	Dave Jiang <dave.jiang@intel.com>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>,
	Matthew Wilcox <willy@infradead.org>,
	Jason Gunthorpe <jgg@ziepe.ca>, John Hubbard <jhubbard@nvidia.com>,
	Jane Chu <jane.chu@oracle.com>,
	Muchun Song <songmuchun@bytedance.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Linux NVDIMM <nvdimm@lists.linux.dev>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v3 04/14] mm/memremap: add ZONE_DEVICE support for
 compound pages
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References: <20210714193542.21857-1-joao.m.martins@oracle.com>
 <20210714193542.21857-5-joao.m.martins@oracle.com>
 <CAPcyv4jwd_dzTH1H+cbiKqfK5=Xaa9JY=EVKHhPbjicVZA-URQ@mail.gmail.com>
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On Wed, Jul 14, 2021 at 06:08:14PM -0700, Dan Williams wrote:
> > +static inline unsigned long pgmap_geometry(struct dev_pagemap *pgmap)
> > +{
> > +       if (!pgmap || !pgmap->geometry)
> > +               return PAGE_SIZE;
> > +       return pgmap->geometry;
> > +}
> > +
> > +static inline unsigned long pgmap_pfn_geometry(struct dev_pagemap *pgmap)
> > +{
> > +       return PHYS_PFN(pgmap_geometry(pgmap));
> > +}
> 
> Are both needed? Maybe just have ->geometry natively be in nr_pages
> units directly, because pgmap_pfn_geometry() makes it confusing
> whether it's a geometry of the pfn or the geometry of the pgmap.

Actually - do we need non-power of two sizes here?  Otherwise a shift
for the pfns would be really nice as that simplifies a lot of the
calculations.