linux-kernel - Re: [PATCH v2 12/19] btrfs: Convert btrfs_migratepage to migrate

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Date:   Thu, 9 Jun 2022 18:40:28 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     dsterba@...e.cz, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-aio@...ck.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        cluster-devel@...hat.com, linux-mm@...ck.org,
        linux-xfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net, ocfs2-devel@....oracle.com,
        linux-mtd@...ts.infradead.org,
        virtualization@...ts.linux-foundation.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 12/19] btrfs: Convert btrfs_migratepage to
 migrate_folio

On Thu, Jun 09, 2022 at 06:33:23PM +0200, David Sterba wrote:
> On Wed, Jun 08, 2022 at 04:02:42PM +0100, Matthew Wilcox (Oracle) wrote:
> > Use filemap_migrate_folio() to do the bulk of the work, and then copy
> > the ordered flag across if needed.
> > 
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> > Reviewed-by: Christoph Hellwig <hch@....de>
> 
> Acked-by: David Sterba <dsterba@...e.com>
> 
> > +static int btrfs_migrate_folio(struct address_space *mapping,
> > +			     struct folio *dst, struct folio *src,
> >  			     enum migrate_mode mode)
> >  {
> > -	int ret;
> > +	int ret = filemap_migrate_folio(mapping, dst, src, mode);
> >  
> > -	ret = migrate_page_move_mapping(mapping, newpage, page, 0);
> >  	if (ret != MIGRATEPAGE_SUCCESS)
> >  		return ret;
> >  
> > -	if (page_has_private(page))
> > -		attach_page_private(newpage, detach_page_private(page));
> 
> If I'm reading it correctly, the private pointer does not need to be set
> like that anymore because it's done somewhere during the
> filemap_migrate_folio() call.

That's correct.  Everything except moving the ordered flag across is
done for you, and I'm kind of tempted to modify folio_migrate_flags()
to copy the ordered flag across as well.  Then you could just use
filemap_migrate_folio() directly.

> > -
> > -	if (PageOrdered(page)) {
> > -		ClearPageOrdered(page);
> > -		SetPageOrdered(newpage);
> > +	if (folio_test_ordered(src)) {
> > +		folio_clear_ordered(src);
> > +		folio_set_ordered(dst);
> >  	}