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

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Date:   Wed, 16 Nov 2022 19:20:40 +0100
From:   Jan Kara <jack@...e.cz>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jan Kara <jack@...e.cz>, 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 ->writepageo      

On Wed 16-11-22 08:14:15, Christoph Hellwig wrote:
> 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.

Right.

> 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.

Looking at the code, IMO the write_one_page() looks somewhat premature
anyway in that place. AFAICS we could handle the writeout using
filemap_write_and_wait() if we moved it to somewhat later moment. So
something like attached patch (only basic testing only so far)?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

View attachment "0001-ext2-Don-t-flush-page-immediately-for-DIRSYNC-direct.patch" of type "text/x-patch" (3882 bytes)