[RFC PATCH 2/5] mm: add folios_copy() for copying pages in batch during migration

[Shivank Garg <shivankg@xxxxxxx>]

This patch introduces the folios_copy() function to copy the folio content
from the list of src folios to the list of dst folios. This is preparatory
patch for batch page migration offloading.

Signed-off-by: Shivank Garg <shivankg@xxxxxxx>
---
 include/linux/mm.h |  1 +
 mm/util.c          | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f5a97dec5169..cd5f37ec72f0 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1300,6 +1300,7 @@ void put_pages_list(struct list_head *pages);
 
 void split_page(struct page *page, unsigned int order);
 void folio_copy(struct folio *dst, struct folio *src);
+void folios_copy(struct list_head *dst_list, struct list_head *src_list);
 
 unsigned long nr_free_buffer_pages(void);
 
diff --git a/mm/util.c b/mm/util.c
index 5a6a9802583b..3a278db28429 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -811,6 +811,28 @@ void folio_copy(struct folio *dst, struct folio *src)
 }
 EXPORT_SYMBOL(folio_copy);
 
+/**
+ * folios_copy - Copy the contents of list of folios.
+ * @dst_list: Folios to copy to.
+ * @src_list: Folios to copy from.
+ *
+ * The folio contents are copied from @src_list to @dst_list.
+ * Assume the caller has validated that lists are not empty and both lists
+ * have equal number of folios. This may sleep.
+ */
+void folios_copy(struct list_head *dst_list,
+		struct list_head *src_list)
+{
+	struct folio *src, *dst;
+
+	dst = list_first_entry(dst_list, struct folio, lru);
+	list_for_each_entry(src, src_list, lru) {
+		cond_resched();
+		folio_copy(dst, src);
+		dst = list_next_entry(dst, lru);
+	}
+}
+
 int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;
 int sysctl_overcommit_ratio __read_mostly = 50;
 unsigned long sysctl_overcommit_kbytes __read_mostly;
-- 
2.34.1