linux-kernel - [PATCH 3/3] mm/memory_hotplug: Refactor hotadd_init_pgdat and try_online

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Date:   Mon,  7 Mar 2022 16:07:25 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Wei Yang <richard.weiyang@...il.com>,
        Miaohe Lin <linmiaohe@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Oscar Salvador <osalvador@...e.de>
Subject: [PATCH 3/3] mm/memory_hotplug: Refactor hotadd_init_pgdat and try_online_node

Since we pre-allocate all nodes now, hotadd_init_pgdat() does
not need to return a pgdat struct, as that was meant for
__try_online_node() to check whether the node was succesfully
allocated.

Also get rid of the __ref as all functions hotadd_init_pgdat()
calls fall within the same section.

Also try to make more clear the return codes from __try_online_node().
__try_online_node() can return either 0, 1 or -errno (the latter not really
as the BUG_ON() would catch it before we return) but depending on the caller
that has different meanings.
For add_memory_resource(), when __try_online_node() returns non-zero,
it means that the node was already allocated and it does not need to bring
it up. It is fine not to check for -errno values because we do not
get to call register_one_node() when !set_node_online.
For those who call try_online_node(), so set_node_online is true, a value
other than zero means a failure (e.g: cpu_up() or find_and_online_cpu_nid()).

Signed-off-by: Oscar Salvador <osalvador@...e.de>
---
 mm/memory_hotplug.c | 35 ++++++++++++++---------------------
 1 file changed, 14 insertions(+), 21 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 07cece9e22e4..5c92ac81a399 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1161,8 +1161,7 @@ static void reset_node_present_pages(pg_data_t *pgdat)
 	pgdat->node_present_pages = 0;
 }
 
-/* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
-static pg_data_t __ref *hotadd_init_pgdat(int nid)
+static void hotadd_init_pgdat(int nid)
 {
 	struct pglist_data *pgdat = NODE_DATA(nid);
 
@@ -1182,8 +1181,6 @@ static pg_data_t __ref *hotadd_init_pgdat(int nid)
 	 * to access not-initialized zonelist, build here.
 	 */
 	build_all_zonelists(pgdat);
-
-	return pgdat;
 }
 
 /*
@@ -1193,31 +1190,27 @@ static pg_data_t __ref *hotadd_init_pgdat(int nid)
  * called by cpu_up() to online a node without onlined memory.
  *
  * Returns:
- * 1 -> a new node has been allocated
- * 0 -> the node is already online
- * -ENOMEM -> the node could not be allocated
+ * 1 -> The node has been initialized.
+ * 0 -> Either the node was already online, or we succesfully registered a new
+ *      one.
+ * -errno -> register_one_node() failed.
  */
 static int __try_online_node(int nid, bool set_node_online)
 {
-	pg_data_t *pgdat;
-	int ret = 1;
+	int ret;
 
 	if (node_online(nid))
 		return 0;
 
-	pgdat = hotadd_init_pgdat(nid);
-	if (!pgdat) {
-		pr_err("Cannot online node %d due to NULL pgdat\n", nid);
-		ret = -ENOMEM;
-		goto out;
-	}
+	hotadd_init_pgdat(nid);
+
+	if (!set_node_online)
+		return 1;
+
+	node_set_online(nid);
+	ret = register_one_node(nid);
+	BUG_ON(ret);
 
-	if (set_node_online) {
-		node_set_online(nid);
-		ret = register_one_node(nid);
-		BUG_ON(ret);
-	}
-out:
 	return ret;
 }
 
-- 
2.34.1