From: Christoph Hellwig <firstname.lastname@example.org> To: Dave Chinner <email@example.com> Cc: Christoph Hellwig <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: xfs: untangle the direct I/O and DAX path, fix DAX locking Date: Fri, 24 Jun 2016 09:26:12 +0200 Message-ID: <20160624072612.GA22205@lst.de> (raw) In-Reply-To: <20160623232446.GA12670@dastard> On Fri, Jun 24, 2016 at 09:24:46AM +1000, Dave Chinner wrote: > Except we did that *intentionally* - by definition there is no > cache to bypass with DAX and so all IO is "direct". That, combined > with the fact that all Linux filesystems except XFS break the POSIX > exclusive writer rule you are quoting to begin with, it seemed > pointless to enforce it for DAX.... No file system breaks the exclusive writer rule - most filesystem don't make writers atomic vs readers. More importantly every other filesystem (well there only are ext2 and ext4..) exludes DAX writers against other DAX writers. > So, before taking any patches to change that behaviour in XFS, a > wider discussion about the policy needs to be had. I don't think > we should care about POSIX here - if you have an application that > needs this serialisation, turn off DAX. That's why I made it a > per-inode inheritable flag and why the mount option will go away > over time. Sorry, but this is simply broken - allowing apps to opt-in behavior (e.g. like we're using O_DIRECT) is always fine. Requriring filesystem-specific tuning that has affect outside the app to get existing documented behavior is not how to design APIs. Maybe we'll need to opt-in to use DAX for mmap, but giving the same existing behavior for read and write and avoiding a copy to the pagecache is an obvious win.
next prev parent reply index Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-06-22 15:27 Christoph Hellwig 2016-06-22 15:27 ` [PATCH 1/8] xfs: don't pass ioflags around in the ioctl path Christoph Hellwig 2016-06-22 15:27 ` [PATCH 2/8] xfs: kill ioflags Christoph Hellwig 2016-06-22 15:27 ` [PATCH 3/8] xfs: remove s_maxbytes enforcement in xfs_file_read_iter Christoph Hellwig 2016-06-22 15:27 ` [PATCH 4/8] xfs: split xfs_file_read_iter into buffered and direct I/O helpers Christoph Hellwig 2016-06-22 15:27 ` [PATCH 5/8] xfs: stop using generic_file_read_iter for direct I/O Christoph Hellwig 2016-06-22 15:27 ` [PATCH 6/8] xfs: direct calls in the direct I/O path Christoph Hellwig 2016-06-22 15:27 ` [PATCH 7/8] xfs: split direct I/O and DAX path Christoph Hellwig 2016-09-29 2:53 ` Darrick J. Wong 2016-09-29 8:38 ` aio completions vs file_accessed race, was: " Christoph Hellwig 2016-09-29 20:18 ` Christoph Hellwig 2016-09-29 20:18 ` Christoph Hellwig 2016-09-29 20:33 ` Darrick J. Wong 2016-06-22 15:27 ` [PATCH 8/8] xfs: fix locking for DAX writes Christoph Hellwig 2016-06-23 14:22 ` Boaz Harrosh 2016-06-23 23:24 ` xfs: untangle the direct I/O and DAX path, fix DAX locking Dave Chinner 2016-06-24 1:14 ` Dan Williams 2016-06-24 7:13 ` Dave Chinner 2016-06-24 7:31 ` Christoph Hellwig 2016-06-24 7:26 ` Christoph Hellwig [this message] 2016-06-24 23:00 ` Dave Chinner 2016-06-28 13:10 ` Christoph Hellwig 2016-06-28 13:27 ` Boaz Harrosh 2016-06-28 13:39 ` Christoph Hellwig 2016-06-28 13:56 ` Boaz Harrosh 2016-06-28 15:39 ` Christoph Hellwig 2016-06-29 12:23 ` Boaz Harrosh
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