[PATCH 5/5] mm/hotplug: export try_online_node

["Alastair D'Silva" <alastair@au1.ibm.com>]

From: Alastair D'Silva <alastair@d-silva.org>

If an external driver module supplies physical memory and needs to expose
the memory on a specific NUMA node, it needs to be able to call
try_online_node to allocate the data structures for the node.

The previous assertion that all callers want to online the node, and that
the provided memory address starts at 0 is no longer true, so these
parameters must alse be exposed.

Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
---
 include/linux/memory_hotplug.h |  4 ++--
 kernel/cpu.c                   |  2 +-
 mm/memory_hotplug.c            | 20 +++++++++++++++-----
 3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index ae892eef8b82..9272e7955541 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -109,7 +109,7 @@ extern void __online_page_set_limits(struct page *page);
 extern void __online_page_increment_counters(struct page *page);
 extern void __online_page_free(struct page *page);
 
-extern int try_online_node(int nid);
+int try_online_node(int nid, u64 start, bool set_node_online);
 
 extern int arch_add_memory(int nid, u64 start, u64 size,
 			struct mhp_restrictions *restrictions);
@@ -274,7 +274,7 @@ static inline void register_page_bootmem_info_node(struct pglist_data *pgdat)
 {
 }
 
-static inline int try_online_node(int nid)
+static inline int try_online_node(int nid, u64 start, bool set_node_online)
 {
 	return 0;
 }
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 077fde6fb953..ffe5f7239a5c 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1167,7 +1167,7 @@ static int do_cpu_up(unsigned int cpu, enum cpuhp_state target)
 		return -EINVAL;
 	}
 
-	err = try_online_node(cpu_to_node(cpu));
+	err = try_online_node(cpu_to_node(cpu), 0, true);
 	if (err)
 		return err;
 
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 382b3a0c9333..9c2784f89e60 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1004,7 +1004,7 @@ static void rollback_node_hotadd(int nid)
 
 
 /**
- * try_online_node - online a node if offlined
+ * __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
@@ -1039,18 +1039,28 @@ static int __try_online_node(int nid, u64 start, bool set_node_online)
 	return ret;
 }
 
-/*
- * Users of this function always want to online/register the node
+/**
+ * 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.
+ *
+ * Returns:
+ * 1 -> a new node has been allocated
+ * 0 -> the node is already online
+ * -ENOMEM -> the node could not be allocated
  */
-int try_online_node(int nid)
+int try_online_node(int nid, u64 start, bool set_node_online)
 {
 	int ret;
 
 	mem_hotplug_begin();
-	ret =  __try_online_node(nid, 0, true);
+	ret =  __try_online_node(nid, start, set_node_online);
 	mem_hotplug_done();
 	return ret;
 }
+EXPORT_SYMBOL_GPL(try_online_node);
 
 static int check_hotplug_memory_range(u64 start, u64 size)
 {
-- 
2.21.0