# Re: \[PATCH v3 04/14\] mm/memremap: add ZONE\_DEVICE support for compound pages

- From: Christoph Hellwig \<hch@infradead.org\>
- Date: 2021-07-15 06:50:21 
- List: linux-doc
- Page: https://ratatoskr.run/linux-doc/2021/07/6509856
- Thread: https://ratatoskr.run/linux-mm/2021/07/6509813/t.md

```text
> +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);

```