linux-ext4 - Re: [PATCH] ext4: don't unconditionally zero blocks on dax writes

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Message-ID: <8a714ec4-1584-6aba-a736-605add8fa0ed@redhat.com>
Date:   Wed, 20 Sep 2017 17:37:07 -0500
From:   Eric Sandeen <sandeen@...hat.com>
To:     "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        Jan Kara <jack@...e.cz>
Subject: Re: [PATCH] ext4: don't unconditionally zero blocks on dax writes

On 9/20/17 4:44 PM, Eric Sandeen wrote:
> The conversion to iomap seems to have lost the ability to
> conditionally /not/ prezero dax blocks.  This leads to
> double writes which cuts throughput in half in some
> cases.
> 
> This puts back the old conditional zeroing logic.
> 
> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
> ---
> 
> I might be completely missing something here, i.e. whether
> the change may have been intentional, etc.  The patch is
> only lightly tested but a which check here seems to DTRT.

Whoops, dchinner tells me this is intentional to avoid a data
exposure - sorry if I missed prior conversations about the issue.

Self-NAK on this, I guess.

-Eric