mm/memory_hotplug.c: use PFN_UP / PFN_DOWN in walk_system_ram_range()

Patch series "mm/memory_hotplug: online_pages() cleanups", v2.

Some cleanups (+ one fix for a special case) in the context of
online_pages().

This patch (of 5):

This makes it clearer that we will never call func() with duplicate PFNs
in case we have multiple sub-page memory resources.  All unaligned parts
of PFNs are completely discarded.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Reviewed-by: Wei Yang <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Nadav Amit <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Arun KS <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/resource.c

@@ -487,8 +487,8 @@ int walk_system_ram_range(unsigned long start_pfn, unsigned long nr_pages,
 	while (start < end &&
 	       !find_next_iomem_res(start, end, flags, IORES_DESC_NONE,
 				    false, &res)) {
-		pfn = (res.start + PAGE_SIZE - 1) >> PAGE_SHIFT;
-		end_pfn = (res.end + 1) >> PAGE_SHIFT;
+		pfn = PFN_UP(res.start);
+		end_pfn = PFN_DOWN(res.end + 1);
 		if (end_pfn > pfn)
 			ret = (*func)(pfn, end_pfn - pfn, arg);
 		if (ret)