[PATCH 1/6] mm: migration: Factor out code to compute expected number of page references

Jan Kara
2018-12-11T17:21:51Z

Factor out function to compute number of expected page references in
migrate_page_move_mapping(). Note that we move hpage_nr_pages() and
page_has_private() checks from under xas_lock_irq() however this is safe
since we hold page lock.

Signed-off-by: Jan Kara <jack@suse.cz>
---
mm/migrate.c | 27 +++++++++++++++++----------
1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index f7e4bfdc13b7..789c7bc90a0c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -428,6 +428,22 @@ static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
}
#endif /* CONFIG_BLOCK */

+static int expected_page_refs(struct page *page)
+{
+ int expected_count = 1;
+
+ /*
+ * Device public or private pages have an extra refcount as they are
+ * ZONE_DEVICE pages.
+ */
+ expected_count += is_device_private_page(page);
+ expected_count += is_device_public_page(page);
+ if (page->mapping)
+ expected_count += hpage_nr_pages(page) + page_has_private(page);
+
+ return expected_count;
+}
+
/*
* Replace the page in the mapping.
*
@@ -444,14 +460,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
XA_STATE(xas, &mapping->i_pages, page_index(page));
struct zone *oldzone, *newzone;
int dirty;
- int expected_count = 1 + extra_count;
-
- /*
- * Device public or private pages have an extra refcount as they are
- * ZONE_DEVICE pages.
- */
- expected_count += is_device_private_page(page);
- expected_count += is_device_public_page(page);
+ int expected_count = expected_page_refs(page) + extra_count;

if (!mapping) {
/* Anonymous page without mapping */
@@ -471,8 +480,6 @@ int migrate_page_move_mapping(struct address_space *mapping,
newzone = page_zone(newpage);

xas_lock_irq(&xas);
-
- expected_count += hpage_nr_pages(page) + page_has_private(page);
if (page_count(page) != expected_count || xas_load(&xas) != page) {
xas_unlock_irq(&xas);
return -EAGAIN;
--
2.16.4