linux-ext4 - Re: fallocate(FALLOC_FL_ZERO_RANGE_BUT_REALLY) to avoid unwritten extents?

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Date:   Tue, 12 Jan 2021 13:36:33 -0800
From:   Andres Freund <andres@...razel.de>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     Andreas Dilger <adilger@...ger.ca>,
        Christoph Hellwig <hch@...radead.org>,
        Avi Kivity <avi@...lladb.com>, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-block@...r.kernel.org
Subject: Re: fallocate(FALLOC_FL_ZERO_RANGE_BUT_REALLY) to avoid unwritten
 extents?

Hi,

On 2021-01-12 13:14:45 -0800, Darrick J. Wong wrote:
> ALLOCSP64 can only allocate pre-zeroed blocks as part of extending EOF,
> whereas a new FZERO flag means that we can pre-zero an arbitrary range
> of bytes in a file.  I don't know if Avi or Andres' usecases demand that
> kind of flexibilty but I know I'd rather go for the more powerful
> interface.

Postgres/I don't at the moment have a need to allocate "written" zeroed
space anywhere but EOF. I can see some potential uses for more flexible
pre-zeroing in the future though, but not very near term.

Greetings,

Andres Freund