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From: Christoph Hellwig <hch@infradead.org>
To: Brian Foster <bfoster@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>,
	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: Tue, 27 Oct 2020 18:07:31 +0000	[thread overview]
Message-ID: <20201027180731.GA32577@infradead.org> (raw)
In-Reply-To: <20201019165501.GA1232435@bfoster>

On Mon, Oct 19, 2020 at 12:55:01PM -0400, Brian Foster wrote:
> 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.

True.  I guess we need to go back and do another lookup to fully
solve this problem.  That doesn't change my opinion that this patch
makes the problem worse.

  reply	other threads:[~2020-10-27 18:07 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-12 14:03 [PATCH 0/2] iomap: zero dirty pages over unwritten extents 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
2020-10-27 18:07       ` Christoph Hellwig [this message]
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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