linux-ext4 - Re: [PATCH v2 12/19] btrfs: Convert btrfs_migratepage to migrate

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Date:   Fri, 10 Jun 2022 01:05:01 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     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 06:40:28PM +0100, Matthew Wilcox wrote:
> 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.

Either way it works for me. If it would mean an unsafe change in folios
or complicate other code I'm fine with the migration callback that
does additional work for btrfs that could be changed later.