mm: factor out next_present_section_nr()

Let's move it to the header and use the shorter variant from
mm/page_alloc.c (the original one will also check
"__highest_present_section_nr + 1", which is not necessary).  While at
it, make the section_nr in next_pfn() const.

In next_pfn(), we now return section_nr_to_pfn(-1) instead of -1 once we
exceed __highest_present_section_nr, which doesn't make a difference in
the caller as it is big enough (>= all sane end_pfn).

Link: http://lkml.kernel.org/r/20200113144035.10848-3-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: "Jin, Zhi" <zhi.jin@intel.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmzone.h

@@ -1379,6 +1379,16 @@ static inline int pfn_present(unsigned long pfn)
 	return present_section(__nr_to_section(pfn_to_section_nr(pfn)));
 }
 
+static inline unsigned long next_present_section_nr(unsigned long section_nr)
+{
+	while (++section_nr <= __highest_present_section_nr) {
+		if (present_section_nr(section_nr))
+			return section_nr;
+	}
+
+	return -1;
+}
+
 /*
  * These are _only_ used during initialisation, therefore they
  * can use __initdata ...  They could have names to indicate

mm/page_alloc.c

@@ -5852,18 +5852,11 @@ overlap_memmap_init(unsigned long zone, unsigned long *pfn)
 /* Skip PFNs that belong to non-present sections */
 static inline __meminit unsigned long next_pfn(unsigned long pfn)
 {
-	unsigned long section_nr;
+	const unsigned long section_nr = pfn_to_section_nr(++pfn);
 
-	section_nr = pfn_to_section_nr(++pfn);
 	if (present_section_nr(section_nr))
 		return pfn;
-
-	while (++section_nr <= __highest_present_section_nr) {
-		if (present_section_nr(section_nr))
-			return section_nr_to_pfn(section_nr);
-	}
-
-	return -1;
+	return section_nr_to_pfn(next_present_section_nr(section_nr));
 }
 #else
 static inline __meminit unsigned long next_pfn(unsigned long pfn)

mm/sparse.c

@@ -198,16 +198,6 @@ static void section_mark_present(struct mem_section *ms)
 	ms->section_mem_map |= SECTION_MARKED_PRESENT;
 }
 
-static inline unsigned long next_present_section_nr(unsigned long section_nr)
-{
-	do {
-		section_nr++;
-		if (present_section_nr(section_nr))
-			return section_nr;
-	} while ((section_nr <= __highest_present_section_nr));
-
-	return -1;
-}
 #define for_each_present_section_nr(start, section_nr)		\
 	for (section_nr = next_present_section_nr(start-1);	\
 	     ((section_nr != -1) &&				\