[PATCH v9 03/12] mm/hotplug: Prepare shrink_{zone, pgdat}_span for sub-section removal

[Dan Williams]

Sub-section hotplug support reduces the unit of operation of hotplug
from section-sized-units (PAGES_PER_SECTION) to sub-section-sized units
(PAGES_PER_SUBSECTION). Teach shrink_{zone,pgdat}_span() to consider
PAGES_PER_SUBSECTION boundaries as the points where pfn_valid(), not
valid_section(), can toggle.

Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Reviewed-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 mm/memory_hotplug.c |   29 ++++++++---------------------
 1 file changed, 8 insertions(+), 21 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 7b963c2d3a0d..647859a1d119 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -318,12 +318,8 @@ static unsigned long find_smallest_section_pfn(int nid, struct zone *zone,
 				     unsigned long start_pfn,
 				     unsigned long end_pfn)
 {
-	struct mem_section *ms;
-
-	for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SECTION) {
-		ms = __pfn_to_section(start_pfn);
-
-		if (unlikely(!valid_section(ms)))
+	for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) {
+		if (unlikely(!pfn_valid(start_pfn)))
 			continue;
 
 		if (unlikely(pfn_to_nid(start_pfn) != nid))
@@ -343,15 +339,12 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
 				    unsigned long start_pfn,
 				    unsigned long end_pfn)
 {
-	struct mem_section *ms;
 	unsigned long pfn;
 
 	/* pfn is the end pfn of a memory section. */
 	pfn = end_pfn - 1;
-	for (; pfn >= start_pfn; pfn -= PAGES_PER_SECTION) {
-		ms = __pfn_to_section(pfn);
-
-		if (unlikely(!valid_section(ms)))
+	for (; pfn >= start_pfn; pfn -= PAGES_PER_SUBSECTION) {
+		if (unlikely(!pfn_valid(pfn)))
 			continue;
 
 		if (unlikely(pfn_to_nid(pfn) != nid))
@@ -373,7 +366,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
 	unsigned long z = zone_end_pfn(zone); /* zone_end_pfn namespace clash */
 	unsigned long zone_end_pfn = z;
 	unsigned long pfn;
-	struct mem_section *ms;
 	int nid = zone_to_nid(zone);
 
 	zone_span_writelock(zone);
@@ -410,10 +402,8 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
 	 * it check the zone has only hole or not.
 	 */
 	pfn = zone_start_pfn;
-	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SECTION) {
-		ms = __pfn_to_section(pfn);
-
-		if (unlikely(!valid_section(ms)))
+	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUBSECTION) {
+		if (unlikely(!pfn_valid(pfn)))
 			continue;
 
 		if (page_zone(pfn_to_page(pfn)) != zone)
@@ -441,7 +431,6 @@ static void shrink_pgdat_span(struct pglist_data *pgdat,
 	unsigned long p = pgdat_end_pfn(pgdat); /* pgdat_end_pfn namespace clash */
 	unsigned long pgdat_end_pfn = p;
 	unsigned long pfn;
-	struct mem_section *ms;
 	int nid = pgdat->node_id;
 
 	if (pgdat_start_pfn == start_pfn) {
@@ -478,10 +467,8 @@ static void shrink_pgdat_span(struct pglist_data *pgdat,
 	 * has only hole or not.
 	 */
 	pfn = pgdat_start_pfn;
-	for (; pfn < pgdat_end_pfn; pfn += PAGES_PER_SECTION) {
-		ms = __pfn_to_section(pfn);
-
-		if (unlikely(!valid_section(ms)))
+	for (; pfn < pgdat_end_pfn; pfn += PAGES_PER_SUBSECTION) {
+		if (unlikely(!pfn_valid(pfn)))
 			continue;
 
 		if (pfn_to_nid(pfn) != nid)