Re: [PATCH 10/10] mm/migrate.c: call detach_page_private to cleanup code

[Guoqing Jiang]

On 5/23/20 1:53 AM, Andrew Morton wrote:

On Fri, 22 May 2020 09:18:25 +0200 Guoqing Jiang 
<guoqing.ji...@cloud.ionos.com> wrote:

-       ClearPagePrivate(page);
-       set_page_private(newpage, page_private(page));
-       set_page_private(page, 0);
-       put_page(page);
+       set_page_private(newpage, detach_page_private(page));

attach_page_private(newpage, detach_page_private(page));

Mattew had suggested it as follows, but not sure if we can reorder of
the setup of
the bh and setting PagePrivate, so I didn't want to break the original
syntax.

@@ -797,11 +797,7 @@ static int __buffer_migrate_page(struct address_space 
*mapping,
          if (rc != MIGRATEPAGE_SUCCESS)
                  goto unlock_buffers;

- ClearPagePrivate(page);

-       set_page_private(newpage, page_private(page));
-       set_page_private(page, 0);
-       put_page(page);
-       get_page(newpage);
+       attach_page_private(newpage, detach_page_private(page));

bh = head;

          do {
@@ -810,8 +806,6 @@ static int __buffer_migrate_page(struct address_space 
*mapping,

} while (bh != head); - SetPagePrivate(newpage);

-
          if (mode != MIGRATE_SYNC_NO_COPY)

This is OK - coherency between PG_private and the page's buffer
ring is maintained by holding lock_page().

Appreciate for your explanation.

Thanks,
Guoqing

I have (effectively) applied the above change.