[PATCH v6 04/12] 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>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 include/linux/mmzone.h |    2 ++
 mm/memory_hotplug.c    |   16 ++++++++--------
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index cffde898e345..b13f0cddf75e 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1164,6 +1164,8 @@ static inline unsigned long section_nr_to_pfn(unsigned long sec)
 
 #define SECTION_ACTIVE_SIZE ((1UL << SECTION_SIZE_BITS) / BITS_PER_LONG)
 #define SECTION_ACTIVE_MASK (~(SECTION_ACTIVE_SIZE - 1))
+#define PAGES_PER_SUB_SECTION (SECTION_ACTIVE_SIZE / PAGE_SIZE)
+#define PAGE_SUB_SECTION_MASK (~(PAGES_PER_SUB_SECTION-1))
 
 struct mem_section_usage {
 	/*
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 8b7415736d21..d5874f9d4043 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -327,10 +327,10 @@ static unsigned long find_smallest_section_pfn(int nid, struct zone *zone,
 {
 	struct mem_section *ms;
 
-	for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SECTION) {
+	for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUB_SECTION) {
 		ms = __pfn_to_section(start_pfn);
 
-		if (unlikely(!valid_section(ms)))
+		if (unlikely(!pfn_valid(start_pfn)))
 			continue;
 
 		if (unlikely(pfn_to_nid(start_pfn) != nid))
@@ -355,10 +355,10 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
 
 	/* pfn is the end pfn of a memory section. */
 	pfn = end_pfn - 1;
-	for (; pfn >= start_pfn; pfn -= PAGES_PER_SECTION) {
+	for (; pfn >= start_pfn; pfn -= PAGES_PER_SUB_SECTION) {
 		ms = __pfn_to_section(pfn);
 
-		if (unlikely(!valid_section(ms)))
+		if (unlikely(!pfn_valid(pfn)))
 			continue;
 
 		if (unlikely(pfn_to_nid(pfn) != nid))
@@ -417,10 +417,10 @@ 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) {
+	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUB_SECTION) {
 		ms = __pfn_to_section(pfn);
 
-		if (unlikely(!valid_section(ms)))
+		if (unlikely(!pfn_valid(pfn)))
 			continue;
 
 		if (page_zone(pfn_to_page(pfn)) != zone)
@@ -485,10 +485,10 @@ 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) {
+	for (; pfn < pgdat_end_pfn; pfn += PAGES_PER_SUB_SECTION) {
 		ms = __pfn_to_section(pfn);
 
-		if (unlikely(!valid_section(ms)))
+		if (unlikely(!pfn_valid(pfn)))
 			continue;
 
 		if (pfn_to_nid(pfn) != nid)