mm/memory_hotplug.c: cleanup __add_pages()

Let's drop the basically unused section stuff and simplify.  The logic now
matches the logic in __remove_pages().
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Link: http://lkml.kernel.org/r/20200228095819.10750-3-david@redhat.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -307,8 +307,9 @@ static int check_hotplug_memory_addressable(unsigned long pfn,
 int __ref __add_pages(int nid, unsigned long pfn, unsigned long nr_pages,
 		struct mhp_restrictions *restrictions)
 {
+	const unsigned long end_pfn = pfn + nr_pages;
+	unsigned long cur_nr_pages;
 	int err;
-	unsigned long nr, start_sec, end_sec;
 	struct vmem_altmap *altmap = restrictions->altmap;
 
 	err = check_hotplug_memory_addressable(pfn, nr_pages);
@@ -331,18 +332,13 @@ int __ref __add_pages(int nid, unsigned long pfn, unsigned long nr_pages,
 	if (err)
 		return err;
 
-	start_sec = pfn_to_section_nr(pfn);
-	end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
-	for (nr = start_sec; nr <= end_sec; nr++) {
-		unsigned long pfns;
-
-		pfns = min(nr_pages, PAGES_PER_SECTION
-				- (pfn & ~PAGE_SECTION_MASK));
-		err = sparse_add_section(nid, pfn, pfns, altmap);
+	for (; pfn < end_pfn; pfn += cur_nr_pages) {
+		/* Select all remaining pages up to the next section boundary */
+		cur_nr_pages = min(end_pfn - pfn,
+				   SECTION_ALIGN_UP(pfn + 1) - pfn);
+		err = sparse_add_section(nid, pfn, cur_nr_pages, altmap);
 		if (err)
 			break;
-		pfn += pfns;
-		nr_pages -= pfns;
 		cond_resched();
 	}
 	vmemmap_populate_print_last();