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From: Brian Foster <bfoster@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 1/2] iomap: use page dirty state to seek data over unwritten extents
Date: Mon, 19 Oct 2020 12:55:01 -0400
Message-ID: <20201019165501.GA1232435@bfoster> (raw)
In-Reply-To: <20201015094700.GB21420@infradead.org>

On Thu, Oct 15, 2020 at 10:47:00AM +0100, Christoph Hellwig wrote:
> I don't think we can solve this properly.  Due to the racyness we can
> always err one side.  The beauty of treating all the uptodate pages
> as present data is that we err on the safe side, as applications
> expect holes to never have data, while "data" could always be zeroed.
> 

I don't think that's quite accurate. Nothing prevents a dirty page from
being written back and reclaimed between acquiring the (unwritten)
mapping and doing the pagecache scan, so it's possible to present valid
data (written to the kernel prior to a seek) as a hole with the current
code.

Brian


  reply index

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-12 14:03 [PATCH 0/2] iomap: zero dirty pages " Brian Foster
2020-10-12 14:03 ` [PATCH 1/2] iomap: use page dirty state to seek data " Brian Foster
2020-10-13 12:30   ` Brian Foster
2020-10-13 22:53   ` Dave Chinner
2020-10-14 12:59     ` Brian Foster
2020-10-14 22:37       ` Dave Chinner
2020-10-15  9:47   ` Christoph Hellwig
2020-10-19 16:55     ` Brian Foster [this message]
2020-10-27 18:07       ` Christoph Hellwig
2020-10-28 11:31         ` Brian Foster
2020-10-12 14:03 ` [PATCH 2/2] iomap: zero cached pages over unwritten extents on zero range Brian Foster
2020-10-15  9:49   ` Christoph Hellwig
2020-10-19 16:55     ` Brian Foster
2020-10-19 18:01       ` Brian Foster
2020-10-20 16:21         ` Brian Foster
2020-10-27 18:15           ` Christoph Hellwig
2020-10-28 11:31             ` Brian Foster
2020-10-23  1:02   ` [iomap] 11b5156248: xfstests.xfs.310.fail kernel test robot

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