From: Christoph Hellwig <email@example.com> To: Brian Foster <firstname.lastname@example.org> Cc: Christoph Hellwig <email@example.com>, firstname.lastname@example.org, email@example.com 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 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.
next prev parent 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 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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