linux-ext4 - Re: Problems with determining data presence by examining extents?

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Message-ID: <469988.1579279418@warthog.procyon.org.uk>
Date:   Fri, 17 Jan 2020 16:43:38 +0000
From:   David Howells <dhowells@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     dhowells@...hat.com, Qu Wenruo <quwenruo.btrfs@....com>,
        Andreas Dilger <adilger@...ger.ca>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-btrfs <linux-btrfs@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Problems with determining data presence by examining extents?

Christoph Hellwig <hch@....de> wrote:

> File systems usually pad zeroes where they have to, typically for
> sub-blocksize writes.   Disabling this would break data integrity.

I understand that.  I can, however, round up the netfs I/O granule size and
alignment to a multiple of the cachefile I/O block size.  Also, I'm doing DIO,
so I have to use block size multiples.

But if the filesystem can avoid bridging large, appropriately sized and
aligned blocks, then I can use it.

David