[PATCH v3 5/6] migrate: implement migrate_misplaced_folio_batch

[Gregory Price <gourry@gourry.net>]

A common operation in tiering is to migrate multiple pages at once.
The migrate_misplaced_folio function requires one call for each
individual folio.  Expose a batch-variant of the same call for use
when doing batch migrations.

Signed-off-by: Gregory Price <gourry@gourry.net>
---
 include/linux/migrate.h |  5 +++++
 mm/migrate.c            | 31 +++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 29919faea2f1..3dfbe7c1cc83 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -145,6 +145,7 @@ const struct movable_operations *page_movable_ops(struct page *page)
 int migrate_misplaced_folio_prepare(struct folio *folio,
 		struct vm_area_struct *vma, int node);
 int migrate_misplaced_folio(struct folio *folio, int node);
+int migrate_misplaced_folio_batch(struct list_head *foliolist, int node);
 #else
 static inline int migrate_misplaced_folio_prepare(struct folio *folio,
 		struct vm_area_struct *vma, int node)
@@ -155,6 +156,10 @@ static inline int migrate_misplaced_folio(struct folio *folio, int node)
 {
 	return -EAGAIN; /* can't migrate now */
 }
+int migrate_misplaced_folio_batch(struct list_head *foliolist, int node)
+{
+	return -EAGAIN; /* can't migrate now */
+}
 #endif /* CONFIG_NUMA_BALANCING */
 
 #ifdef CONFIG_MIGRATION
diff --git a/mm/migrate.c b/mm/migrate.c
index ea20d9bc4f40..a751a995f2d9 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2705,5 +2705,36 @@ int migrate_misplaced_folio(struct folio *folio, int node)
 	BUG_ON(!list_empty(&migratepages));
 	return nr_remaining ? -EAGAIN : 0;
 }
+
+/*
+ * Batch variant of migrate_misplaced_folio. Attempts to migrate
+ * a folio list to the specified destination.
+ *
+ * Caller is expected to have isolated the folios by calling
+ * migrate_misplaced_folio_prepare(), which will result in an
+ * elevated reference count on the folio.
+ *
+ * This function will un-isolate the folios, dereference them, and
+ * remove them from the list before returning.
+ */
+int migrate_misplaced_folio_batch(struct list_head *folio_list, int node)
+{
+	pg_data_t *pgdat = NODE_DATA(node);
+	unsigned int nr_succeeded;
+	int nr_remaining;
+
+	nr_remaining = migrate_pages(folio_list, alloc_misplaced_dst_folio,
+				     NULL, node, MIGRATE_ASYNC,
+				     MR_NUMA_MISPLACED, &nr_succeeded);
+	if (nr_remaining)
+		putback_movable_pages(folio_list);
+
+	if (nr_succeeded) {
+		count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded);
+		mod_node_page_state(pgdat, PGPROMOTE_SUCCESS, nr_succeeded);
+	}
+	BUG_ON(!list_empty(folio_list));
+	return nr_remaining ? -EAGAIN : 0;
+}
 #endif /* CONFIG_NUMA_BALANCING */
 #endif /* CONFIG_NUMA */
-- 
2.47.1