[RFC V3 3/9] mm: Introduce folios_mc_copy() for batch copying folios

[Shivank Garg <shivankg@amd.com>]

Introduce the folios_mc_copy() 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@amd.com>
---
 include/linux/mm.h |  2 ++
 mm/util.c          | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 1ae97a0b8ec7..383702a819ac 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1187,6 +1187,8 @@ void __folio_put(struct folio *folio);
 void split_page(struct page *page, unsigned int order);
 void folio_copy(struct folio *dst, struct folio *src);
 int folio_mc_copy(struct folio *dst, struct folio *src);
+int folios_mc_copy(struct list_head *dst_list, struct list_head *src_list,
+		 unsigned int __maybe_unused folios_cnt);
 
 unsigned long nr_free_buffer_pages(void);
 
diff --git a/mm/util.c b/mm/util.c
index f814e6a59ab1..2d7758f33fc6 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -748,6 +748,35 @@ int folio_mc_copy(struct folio *dst, struct folio *src)
 }
 EXPORT_SYMBOL(folio_mc_copy);
 
+/**
+ * folios_mc_copy - Copy the contents of list of folios.
+ * @dst_list: Folios to copy to.
+ * @src_list: Folios to copy from.
+ * @folios_cnt: Number of folios in each list (unused).
+ *
+ * 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.
+ */
+int folios_mc_copy(struct list_head *dst_list, struct list_head *src_list,
+		 unsigned int __maybe_unused folios_cnt)
+{
+	struct folio *src, *dst;
+	int ret;
+
+	dst = list_first_entry(dst_list, struct folio, lru);
+	list_for_each_entry(src, src_list, lru) {
+		cond_resched();
+		ret = folio_mc_copy(dst, src);
+		if (ret)
+			return ret;
+		dst = list_next_entry(dst, lru);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(folios_mc_copy);
+
 int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;
 static int sysctl_overcommit_ratio __read_mostly = 50;
 static unsigned long sysctl_overcommit_kbytes __read_mostly;
-- 
2.43.0