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From:   David Hildenbrand <david@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     linux-mm@kvack.org, David Hildenbrand <david@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>, Baoquan He <bhe@redhat.com>,
        Oscar Salvador <osalvador@suse.de>,
        Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Subject: [PATCH RFC 1/2] mm/memory_hotplug: no need to init new pgdat with node_start_pfn
Date:   Thu, 16 Apr 2020 12:47:06 +0200
Message-Id: <20200416104707.20219-2-david@redhat.com>
In-Reply-To: <20200416104707.20219-1-david@redhat.com>
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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 =3D=3D 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 *pgda=
t)
 }
=20
 /* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLU=
G */
-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 =3D PFN_DOWN(start);
=20
 	pgdat =3D NODE_DATA(nid);
 	if (!pgdat) {
@@ -899,9 +898,8 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64=
 start)
 	}
=20
 	/* we can use NODE_DATA(nid) from here */
-
 	pgdat->node_id =3D nid;
-	pgdat->node_start_pfn =3D start_pfn;
+	pgdat->node_start_pfn =3D 0;
=20
 	/* 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 =3D 1;
@@ -953,7 +950,7 @@ static int __try_online_node(int nid, u64 start, bool=
 set_node_online)
 	if (node_online(nid))
 		return 0;
=20
-	pgdat =3D hotadd_new_pgdat(nid, start);
+	pgdat =3D hotadd_new_pgdat(nid);
 	if (!pgdat) {
 		pr_err("Cannot online node %d due to NULL pgdat\n", nid);
 		ret =3D -ENOMEM;
@@ -977,7 +974,7 @@ int try_online_node(int nid)
 	int ret;
=20
 	mem_hotplug_begin();
-	ret =3D  __try_online_node(nid, 0, true);
+	ret =3D  __try_online_node(nid, true);
 	mem_hotplug_done();
 	return ret;
 }
@@ -1031,7 +1028,7 @@ int __ref add_memory_resource(int nid, struct resou=
rce *res)
 	 */
 	memblock_add_node(start, size, nid);
=20
-	ret =3D __try_online_node(nid, start, false);
+	ret =3D __try_online_node(nid, false);
 	if (ret < 0)
 		goto error;
 	new_node =3D ret;
--=20
2.25.1