Re: [PATCH v3 04/14] mm/memremap: add ZONE_DEVICE support for compound pages

On 7/15/21 7:48 AM, Christoph Hellwig wrote:

quoted

+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

Nicer indeed.

But this might be removed, should we follow Dan's suggestion on geometry representing nr
of pages.

quoted

+	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);

Yeap, much readable, thanks for the suggestion.