linux-ext4 - Re: [PATCH 2/9] ext2: remove ->writepage

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Date:   Wed, 16 Nov 2022 08:14:15 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Jan Kara <jack@...e.cz>
Cc:     Christoph Hellwig <hch@....de>,
        Namjae Jeon <linkinjeon@...nel.org>,
        Sungjong Seo <sj1557.seo@...sung.com>,
        Jan Kara <jack@...e.com>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
        Dave Kleikamp <shaggy@...nel.org>,
        Bob Copeland <me@...copeland.com>,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        jfs-discussion@...ts.sourceforge.net,
        linux-karma-devel@...ts.sourceforge.net, linux-mm@...ck.org
Subject: Re: [PATCH 2/9] ext2: remove ->writepage

On Mon, Nov 14, 2022 at 11:49:27AM +0100, Jan Kara wrote:
> On Sun 13-11-22 17:28:55, Christoph Hellwig wrote:
> > ->writepage is a very inefficient method to write back data, and only
> > used through write_cache_pages or a a fallback when no ->migrate_folio
> > method is present.
> > 
> > Signed-off-by: Christoph Hellwig <hch@....de>
> 
> Looks good! Feel free to add:

The testbot found a problem with this:

ext2_commit_chunk calls write_one_page for the IS_DIRSYNC case,
and write_one_page calls ->writepage.

So I think I need to drop this one for now (none of the other
file systems calls write_one_page).  And then think what best
to do about write_one_page/write_one_folio.  I suspect just
passing a writepage pointer to them might make most sense,
as they are only used by a few file systems, and the calling
convention with the locked page doesn't lend itself to using
->writepages.