[PATCH rfc 6/9] mm: migrate: support poisoned recover from migrate folio

[Kefeng Wang <wangkefeng.wang@huawei.com>]

In order to support poisoned folio copy recover from migrate folio,
let's use folio_mc_copy() and move it in the begin of the function
of __migrate_folio(), which could simply error handling since there
is no turning back if folio_migrate_mapping() return success, the
downside is the folio copied even though folio_migrate_mapping()
return fail, a small optimization is to check whether folio does
not have extra refs before we do more work ahead in __migrate_folio(),
which could help us avoid unnecessary folio copy.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 mm/migrate.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 107965bbc852..99286394b5e5 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -661,6 +661,14 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,
 {
 	int rc;
 
+	/* Check whether src does not have extra refs before we do more work */
+	if (folio_ref_count(src) != folio_expected_refs(mapping, src))
+		return -EAGAIN;
+
+	rc = folio_mc_copy(dst, src);
+	if (rc)
+		return rc;
+
 	rc = folio_migrate_mapping(mapping, dst, src, 0);
 	if (rc != MIGRATEPAGE_SUCCESS)
 		return rc;
@@ -668,7 +676,7 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,
 	if (src_private)
 		folio_attach_private(dst, folio_detach_private(src));
 
-	folio_migrate_copy(dst, src);
+	folio_migrate_flags(dst, src);
 
 	return MIGRATEPAGE_SUCCESS;
 }
-- 
2.27.0