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SubjectRe: [PATCH 10/10] mm/migrate.c: call detach_page_private to cleanup code
On Fri, 22 May 2020 09:18:25 +0200 Guoqing Jiang <guoqing.jiang@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().

I have (effectively) applied the above change.

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