[PATCH 1/2] mm/ksm: extract helper functions for scan cycle cleanup

["Xu Xin (vivo)" <xu.xin@linux.dev>]

Since scan_get_next_rmap_item() is getting too large, extract two new
helper functions, ksm_prune_migrate_nodes() and ksm_reset_unstable_trees(),
to reduce indentation levels, isolate local variables, and improve the
readability of the main scan loop.

No functional change intended.

Signed-off-by: Xu Xin (vivo) <xu.xin@linux.dev>
---
 mm/ksm.c | 56 +++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 33 insertions(+), 23 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 5e24b5ca8dc8..49977bcf04f7 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2609,6 +2609,37 @@ static struct mm_walk_ops ksm_next_page_ops = {
 	.walk_lock = PGWALK_RDLOCK,
 };
 
+static void ksm_prune_migrate_nodes(void)
+{
+	struct ksm_stable_node *stable_node, *next;
+	struct folio *folio;
+
+	if (ksm_merge_across_nodes)
+		return;
+
+	/*
+	 * Whereas stale stable_nodes on the stable_tree itself
+	 * get pruned in the regular course of stable_tree_search(),
+	 * those moved out to the migrate_nodes list can accumulate:
+	 * so prune them once before each full scan.
+	 */
+	list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
+		folio = ksm_get_folio(stable_node, KSM_GET_FOLIO_NOLOCK);
+
+		if (folio)
+			folio_put(folio);
+		cond_resched();
+	}
+}
+
+static void ksm_reset_unstable_trees(void)
+{
+	int nid;
+
+	for (nid = 0; nid < ksm_nr_node_ids; nid++)
+		root_unstable_tree[nid] = RB_ROOT;
+}
+
 static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 {
 	struct mm_struct *mm;
@@ -2617,7 +2648,6 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 	struct vm_area_struct *vma;
 	struct ksm_rmap_item *rmap_item;
 	struct vma_iterator vmi;
-	int nid;
 
 	if (list_empty(&ksm_mm_head.slot.mm_node))
 		return NULL;
@@ -2639,28 +2669,8 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
 		 */
 		lru_add_drain_all();
 
-		/*
-		 * Whereas stale stable_nodes on the stable_tree itself
-		 * get pruned in the regular course of stable_tree_search(),
-		 * those moved out to the migrate_nodes list can accumulate:
-		 * so prune them once before each full scan.
-		 */
-		if (!ksm_merge_across_nodes) {
-			struct ksm_stable_node *stable_node, *next;
-			struct folio *folio;
-
-			list_for_each_entry_safe(stable_node, next,
-						 &migrate_nodes, list) {
-				folio = ksm_get_folio(stable_node,
-						      KSM_GET_FOLIO_NOLOCK);
-				if (folio)
-					folio_put(folio);
-				cond_resched();
-			}
-		}
-
-		for (nid = 0; nid < ksm_nr_node_ids; nid++)
-			root_unstable_tree[nid] = RB_ROOT;
+		ksm_prune_migrate_nodes();
+		ksm_reset_unstable_trees();
 
 		spin_lock(&ksm_mmlist_lock);
 		slot = list_entry(mm_slot->slot.mm_node.next,
-- 
2.34.1