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Date: Thu, 15 Jul 2021 07:48:52 +0100
From: Christoph Hellwig <hch@infradead.org>
To: Joao Martins <joao.m.martins@oracle.com>
Cc: linux-mm@kvack.org, Dan Williams <dan.j.williams@intel.com>,
	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>, nvdimm@lists.linux.dev,
	linux-doc@vger.kernel.org
Subject: Re: [PATCH v3 04/14] mm/memremap: add ZONE_DEVICE support for
 compound pages
Message-ID: <YO/aVLL2WlWkKXia@infradead.org>
References: <20210714193542.21857-1-joao.m.martins@oracle.com>
 <20210714193542.21857-5-joao.m.martins@oracle.com>
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> +static inline unsigned long pgmap_geometry(struct dev_pagemap *pgmap)
> +{
> +	if (!pgmap || !pgmap->geometry)
> +		return PAGE_SIZE;
> +	return pgmap->geometry;

Nit, but avoiding all the negations would make this a little easier to
read:

	if (pgmap && pgmap->geometry)
		return pgmap->geometry;
	return PAGE_SIZE

> +	if (pgmap_geometry(pgmap) > PAGE_SIZE)
> +		percpu_ref_get_many(pgmap->ref, (pfn_end(pgmap, range_id)
> +			- pfn_first(pgmap, range_id)) / pgmap_pfn_geometry(pgmap));
> +	else
> +		percpu_ref_get_many(pgmap->ref, pfn_end(pgmap, range_id)
> +				- pfn_first(pgmap, range_id));

This is a horrible undreadable mess, which is trivially fixed by a
strategically used local variable:

	refs = pfn_end(pgmap, range_id) - pfn_first(pgmap, range_id);
	if (pgmap_geometry(pgmap) > PAGE_SIZE)
		refs /= pgmap_pfn_geometry(pgmap);
	percpu_ref_get_many(pgmap->ref, refs);