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SubjectRe: [RFC PATCH V2 0/9] Introduce attach/clear_page_private to cleanup code
On Sat, May 02, 2020 at 12:42:15AM +0200, Guoqing Jiang wrote:
> On 5/2/20 12:16 AM, Matthew Wilcox wrote:
> > On Thu, Apr 30, 2020 at 11:44:41PM +0200, Guoqing Jiang wrote:
> > > include/linux/pagemap.h: introduce attach/clear_page_private
> > > md: remove __clear_page_buffers and use attach/clear_page_private
> > > btrfs: use attach/clear_page_private
> > > fs/buffer.c: use attach/clear_page_private
> > > f2fs: use attach/clear_page_private
> > > iomap: use attach/clear_page_private
> > > ntfs: replace attach_page_buffers with attach_page_private
> > > orangefs: use attach/clear_page_private
> > > buffer_head.h: remove attach_page_buffers
> > I think mm/migrate.c could also use this:
> >
> > ClearPagePrivate(page);
> > set_page_private(newpage, page_private(page));
> > set_page_private(page, 0);
> > put_page(page);
> > get_page(newpage);
> >
>
> Thanks for checking!  Assume the below change is appropriate.
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 7160c1556f79..f214adfb3fa4 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -797,10 +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);
> +       set_page_private(newpage, detach_page_private(page));
>         get_page(newpage);

I think you can do:

@@ -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)

... but maybe there's a subtlety to the ordering of the setup of the bh
and setting PagePrivate that means what you have there is a better patch.
Anybody know?
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