Hi Matthew,
On Thu, Aug 05, 2021 at 11:05:56PM +0800, Baolin Wang wrote:
We've got the expected count for anonymous page or file page by
expected_page_refs() at the beginning of migrate_page_move_mapping(),
thus we should move the page count validation a little forward to
reduce duplicated code.
Please add an explanation to the changelog for why it's safe to pull
this out from under the i_pages lock.
Sure. In folio_migrate_mapping(), we are sure that the migration page
was isolated from lru list and locked, so I think there are no race to
get the page count without i_pages lock. Please correct me if I missed
something else. Thanks.
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index 239b238..5559571 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -386,11 +386,10 @@ int folio_migrate_mapping(struct address_space *mapping,
int expected_count = expected_page_refs(mapping, &folio->page) + extra_count;
long nr = folio_nr_pages(folio);
- if (!mapping) {
- /* Anonymous page without mapping */
- if (folio_ref_count(folio) != expected_count)
- return -EAGAIN;
+ if (folio_ref_count(folio) != expected_count)
+ return -EAGAIN;
+ if (!mapping) {
/* No turning back from here */
newfolio->index = folio->index;
newfolio->mapping = folio->mapping;
@@ -404,8 +403,7 @@ int folio_migrate_mapping(struct address_space *mapping,
newzone = folio_zone(newfolio);
xas_lock_irq(&xas);
- if (folio_ref_count(folio) != expected_count ||
- xas_load(&xas) != folio) {
+ if (xas_load(&xas) != folio) {
xas_unlock_irq(&xas);
return -EAGAIN;
}
--
1.8.3.1
