linux-ext4 - Re: [PATCH v5 02/12] ext4: iomap that extends beyond EOF should be marked dirty

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Message-ID: <20191022014917.GB5092@athena.bobrowski.net>
Date:   Tue, 22 Oct 2019 12:49:17 +1100
From:   Matthew Bobrowski <mbobrowski@...browski.org>
To:     Jan Kara <jack@...e.cz>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        hch@...radead.org, david@...morbit.com, darrick.wong@...cle.com
Subject: Re: [PATCH v5 02/12] ext4: iomap that extends beyond EOF should be
 marked dirty

On Mon, Oct 21, 2019 at 03:28:18PM +0200, Jan Kara wrote:
> On Mon 21-10-19 20:17:46, Matthew Bobrowski wrote:
> > This patch is effectively addressed what Dave Chinner had found and
> > fixed within this commit: 8a23414ee345. Justification for needing this
> > modification has been provided below:
> > 
> > When doing a direct IO that spans the current EOF, and there are
> > written blocks beyond EOF that extend beyond the current write, the
> > only metadata update that needs to be done is a file size extension.
> > 
> > However, we don't mark such iomaps as IOMAP_F_DIRTY to indicate that
> > there is IO completion metadata updates required, and hence we may
> > fail to correctly sync file size extensions made in IO completion when
> > O_DSYNC writes are being used and the hardware supports FUA.
> > 
> > Hence when setting IOMAP_F_DIRTY, we need to also take into account
> > whether the iomap spans the current EOF. If it does, then we need to
> > mark it dirty so that IO completion will call generic_write_sync() to
> > flush the inode size update to stable storage correctly.
> > 
> > Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>
> 
> Looks good to me. You could possibly also comment in the changelog that
> currently, this change doesn't have user visible impact for ext4 as none of
> current users of ext4_iomap_begin() that extend files depend of
> IOMAP_F_DIRTY.

Sure, I will add this.

> Also this patch would make slightly more sense to be before 1/12 so that
> you don't have there those two strange unused arguments. But these are just
> small nits.

You're right. I will rearrange it in v6 so that this patch comes
first.

> Feel free to add:
> 
> Reviewed-by: Jan Kara <jack@...e.cz>

Thanks Jan!

--<M>--