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Date:   Tue, 27 Jun 2023 21:56:49 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Eric Sandeen <sandeen@sandeen.net>
Cc:     Masahiko Sawada <sawada.mshk@gmail.com>,
        Dave Chinner <david@fromorbit.com>, linux-xfs@vger.kernel.org
Subject: Re: Question on slow fallocate
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On Tue, Jun 27, 2023 at 11:12:01AM -0500, Eric Sandeen wrote:
> Ok, but what is the reason for zeroing out the blocks prior to them being
> written with real data? I'm wondering what the core requirement here is for
> the zeroing, either via fallocate (which btw posix_fallocate does not
> guarantee) or pwrites of zeros.

Note that even a plain truncate will zero the data visible to the
user.  I could see this tring to reduce fragmentation by making sure
the whole file extension is allocated together insted of split up
as the difference processes write their areas.  But is there data
showing this fragmentation even happens and actually hurts?