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

David Hildenbrand
2020-04-16T10:51:09Z

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@linux-foundation.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
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