[PATCH RFC 1/2] mm/memory_hotplug: no need to init new pgdat with node_start_pfn

[David Hildenbrand <david@xxxxxxxxxx>]

A hotadded node/pgdat will span no pages at all, until memory is moved to
the zone/node via move_pfn_range_to_zone() -> resize_pgdat_range - e.g.,
when onlining memory blocks. We don't have to initialize the
node_start_pfn to the memory we are adding.

Note: we'll also end up with pgdat->node_start_pfn == 0 when offlined the
last memory block belonging to a node (via remove_pfn_range_from_zone()->
update_pgdat_span()).

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 mm/memory_hotplug.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 47cf6036eb31..9b15ce465be2 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -866,10 +866,9 @@ static void reset_node_present_pages(pg_data_t *pgdat)
 }
 
 /* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
-static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
+static pg_data_t __ref *hotadd_new_pgdat(int nid)
 {
 	struct pglist_data *pgdat;
-	unsigned long start_pfn = PFN_DOWN(start);
 
 	pgdat = NODE_DATA(nid);
 	if (!pgdat) {
@@ -899,9 +898,8 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
 	}
 
 	/* we can use NODE_DATA(nid) from here */
-
 	pgdat->node_id = nid;
-	pgdat->node_start_pfn = start_pfn;
+	pgdat->node_start_pfn = 0;
 
 	/* init node's zones as empty zones, we don't have any present pages.*/
 	free_area_init_core_hotplug(nid);
@@ -936,7 +934,6 @@ static void rollback_node_hotadd(int nid)
 /**
  * try_online_node - online a node if offlined
  * @nid: the node ID
- * @start: start addr of the node
  * @set_node_online: Whether we want to online the node
  * called by cpu_up() to online a node without onlined memory.
  *
@@ -945,7 +942,7 @@ static void rollback_node_hotadd(int nid)
  * 0 -> the node is already online
  * -ENOMEM -> the node could not be allocated
  */
-static int __try_online_node(int nid, u64 start, bool set_node_online)
+static int __try_online_node(int nid, bool set_node_online)
 {
 	pg_data_t *pgdat;
 	int ret = 1;
@@ -953,7 +950,7 @@ static int __try_online_node(int nid, u64 start, bool set_node_online)
 	if (node_online(nid))
 		return 0;
 
-	pgdat = hotadd_new_pgdat(nid, start);
+	pgdat = hotadd_new_pgdat(nid);
 	if (!pgdat) {
 		pr_err("Cannot online node %d due to NULL pgdat\n", nid);
 		ret = -ENOMEM;
@@ -977,7 +974,7 @@ int try_online_node(int nid)
 	int ret;
 
 	mem_hotplug_begin();
-	ret =  __try_online_node(nid, 0, true);
+	ret =  __try_online_node(nid, true);
 	mem_hotplug_done();
 	return ret;
 }
@@ -1031,7 +1028,7 @@ int __ref add_memory_resource(int nid, struct resource *res)
 	 */
 	memblock_add_node(start, size, nid);
 
-	ret = __try_online_node(nid, start, false);
+	ret = __try_online_node(nid, false);
 	if (ret < 0)
 		goto error;
 	new_node = ret;
-- 
2.25.1