linux-ext4 - Re: [RFC 1/2] iomap: direct-io: Move inode_dio_begin before filemap_write_and_wait

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Date:   Tue, 14 Jan 2020 10:27:36 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Jan Kara <jack@...e.cz>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [RFC 1/2] iomap: direct-io: Move inode_dio_begin before
 filemap_write_and_wait_range

On Tue, Jan 14, 2020 at 06:19:34PM +0100, Jan Kara wrote:
> We want to detect in the writeback path whether there's direct IO (read)
> currently running for the inode. Not for the writeback issued from
> iomap_dio_rw() but for any arbitrary writeback that iomap_dio_rw() can be
> racing with - so struct writeback_control won't help. Now if you want to
> see the ugly details why this hack is needed, see my other email to Ritesh
> in this thread with details of the race.

How do we get other writeback after iomap_dio_rw wrote everything out?
Either way I'm trying to kill i_dio_count as it has all kinds of
problems, see the patch sent out earlier today.