[PATCH] mm/memory_hotplug: factor out node_is_memoryless()

[Gregory Price]

A memoryless node neither spans present pages (populated or ZONE_DEVICE)
nor has an offline-but-added memory block still linked to it in sysfs.

try_offline_node() presently open-codes this memoryless check.

Pull that into a node_is_memoryless() helper and pull the existing
check_no_memblock_for_node_cb() helper ahead of the add/online path
so it's clearer what is happening here.

No functional change.

Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
---
 mm/memory_hotplug.c | 60 +++++++++++++++++++++++----------------------
 1 file changed, 31 insertions(+), 29 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 226ab9cb078ad..d0e94057682af 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1491,6 +1491,36 @@ static int create_altmaps_and_memory_blocks(int nid, struct memory_group *group,
 	return ret;
 }
 
+static int check_no_memblock_for_node_cb(struct memory_block *mem, void *arg)
+{
+	int nid = *(int *)arg;
+
+	/*
+	 * If a memory block belongs to multiple nodes, the stored nid is not
+	 * reliable. However, such blocks are always online (e.g., cannot get
+	 * offlined) and, therefore, are still spanned by the node.
+	 */
+	return mem->nid == nid ? -EEXIST : 0;
+}
+
+/* Caller must hold the memory hotplug lock for this check. */
+static bool node_is_memoryless(int nid)
+{
+	/*
+	 * A node still spanning pages (especially ZONE_DEVICE) is not
+	 * memoryless.  A node spans memory after move_pfn_range_to_zone(),
+	 * e.g. once a memory block has been onlined.
+	 */
+	if (node_spanned_pages(nid))
+		return false;
+	/*
+	 * Offline memory blocks may not be spanned by the node yet, but they
+	 * link to it in sysfs and can be onlined later, so the node is not
+	 * memoryless while any remain.
+	 */
+	return !for_each_memory_block(&nid, check_no_memblock_for_node_cb);
+}
+
 /*
  * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
  * and online/offline operations (triggered e.g. by sysfs).
@@ -2214,18 +2244,6 @@ static int check_cpu_on_node(int nid)
 	return 0;
 }
 
-static int check_no_memblock_for_node_cb(struct memory_block *mem, void *arg)
-{
-	int nid = *(int *)arg;
-
-	/*
-	 * If a memory block belongs to multiple nodes, the stored nid is not
-	 * reliable. However, such blocks are always online (e.g., cannot get
-	 * offlined) and, therefore, are still spanned by the node.
-	 */
-	return mem->nid == nid ? -EEXIST : 0;
-}
-
 /**
  * try_offline_node
  * @nid: the node ID
@@ -2237,23 +2255,7 @@ static int check_no_memblock_for_node_cb(struct memory_block *mem, void *arg)
  */
 void try_offline_node(int nid)
 {
-	int rc;
-
-	/*
-	 * If the node still spans pages (especially ZONE_DEVICE), don't
-	 * offline it. A node spans memory after move_pfn_range_to_zone(),
-	 * e.g., after the memory block was onlined.
-	 */
-	if (node_spanned_pages(nid))
-		return;
-
-	/*
-	 * Especially offline memory blocks might not be spanned by the
-	 * node. They will get spanned by the node once they get onlined.
-	 * However, they link to the node in sysfs and can get onlined later.
-	 */
-	rc = for_each_memory_block(&nid, check_no_memblock_for_node_cb);
-	if (rc)
+	if (!node_is_memoryless(nid))
 		return;
 
 	if (check_cpu_on_node(nid))
-- 
2.53.0-Meta