From: Ira Weiny <firstname.lastname@example.org> To: Dave Chinner <email@example.com> Cc: Jan Kara <firstname.lastname@example.org>, email@example.com, "Darrick J. Wong" <firstname.lastname@example.org>, Dan Williams <email@example.com>, Christoph Hellwig <firstname.lastname@example.org>, "Theodore Y. Ts'o" <email@example.com>, Jeff Moyer <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: [PATCH V6 7/8] fs/xfs: Change xfs_ioctl_setattr_dax_invalidate() to xfs_ioctl_dax_check() Date: Wed, 8 Apr 2020 15:26:36 -0700 [thread overview] Message-ID: <20200408222636.GC664132@iweiny-DESK2.sc.intel.com> (raw) In-Reply-To: <20200408210950.GL24067@dread.disaster.area> On Thu, Apr 09, 2020 at 07:09:50AM +1000, Dave Chinner wrote: > On Wed, Apr 08, 2020 at 11:58:03AM +0200, Jan Kara wrote: > > On Wed 08-04-20 12:23:18, Dave Chinner wrote: > > > On Tue, Apr 07, 2020 at 11:29:57AM -0700, firstname.lastname@example.org wrote: > > > > From: Ira Weiny <email@example.com> > > > > > > > > We only support changing FS_XFLAG_DAX on directories. Files get their > > > > flag from the parent directory on creation only. So no data > > > > invalidation needs to happen. > > > > > > Which leads me to ask: how are users and/or admins supposed to > > > remove the flag from regular files once it is set in the filesystem? > > > > > > Only being able to override the flag via the "dax=never" mount > > > option means that once the flag is set, nobody can ever remove it > > > and they can only globally turn off dax if it gets set incorrectly. > > > It also means a global interrupt because all apps on the filesystem > > > need to be stopped so the filesystem can be unmounted and mounted > > > again with dax=never. This is highly unfriendly to admins and users. > > > > > > IOWs, we _must_ be able to clear this inode flag on regular inodes > > > in some way. I don't care if it doesn't change the current in-memory > > > state, but we must be able to clear the flags so that the next time > > > the inodes are instantiated DAX is not enabled for those files... > > > > Well, there's one way to clear the flag: delete the file. If you still care > > about the data, you can copy the data first. It isn't very convenient, I > > agree, and effectively means restarting whatever application that is using > > the file. > > Restarting the application is fine. Having to backup/restore or copy > the entire data set just to turn off an inode flag? That's not a > viable management strategy. We could be talking about terabytes of > data here. > > I explained how we can safely remove the flag in the other branch of > this thread... > > > But it seems like more understandable API than letting user clear > > the on-disk flag but the inode will still use DAX until kernel decides to > > evict the inode > > Certainly doesn't seem that way to me. "stop app, clear flags, drop > caches, restart app" is a pretty simple, easy thing to do for an > admin. I want to be clear here: I think this is reasonable. However, I don't see consensus for that interface. Christoph in particular said that a 'lazy change' is: "... straight from the playbook for arcane and confusing API designs." "But returning an error and doing a lazy change anyway is straight from the playbook for arcane and confusing API designs." -- https://lore.kernel.org/lkml/20200403072731.GA24176@lst.de/ Did I somehow misunderstand this? Again for this patch set, 5.8, lets leave that alone for now. I think if we disable setting this on files right now we can still allow it in the future as another step forward. > > Especially compared to process that is effectively "stop app, backup > data set, delete data set, clear flags, restore data set, restart > app" > > > - because that often means you need to restart the > > application using the file anyway for the flag change to have any effect. > > That's a trivial requirement compared to the downtime and resource > cost of a data set backup/restore just to clear inode flags.... > I agree but others do not. This still provides a baby step forward and some granularity for those who plan out the creation of their files. Ira
next prev parent reply other threads:[~2020-04-08 22:26 UTC|newest] Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-04-07 18:29 [PATCH V6 0/8] Enable per-file/per-directory DAX operations V6 ira.weiny 2020-04-07 18:29 ` [PATCH V6 1/8] fs/xfs: Remove unnecessary initialization of i_rwsem ira.weiny 2020-04-07 23:46 ` Dave Chinner 2020-04-07 18:29 ` [PATCH V6 2/8] fs: Remove unneeded IS_DAX() check ira.weiny 2020-04-09 7:31 ` Christoph Hellwig 2020-04-09 14:57 ` Ira Weiny 2020-04-07 18:29 ` [PATCH V6 3/8] fs/stat: Define DAX statx attribute ira.weiny 2020-04-07 23:47 ` Dave Chinner 2020-04-07 18:29 ` [PATCH V6 4/8] fs/xfs: Make DAX mount option a tri-state ira.weiny 2020-04-07 23:59 ` Dave Chinner 2020-04-08 0:09 ` Ira Weiny 2020-04-08 0:48 ` Dave Chinner 2020-04-09 15:03 ` Ira Weiny 2020-04-07 18:29 ` [PATCH V6 5/8] fs/xfs: Create function xfs_inode_enable_dax() ira.weiny 2020-04-08 0:05 ` Dave Chinner 2020-04-08 0:13 ` Ira Weiny 2020-04-07 18:29 ` [PATCH V6 6/8] fs/xfs: Combine xfs_diflags_to_linux() and xfs_diflags_to_iflags() ira.weiny 2020-04-08 2:08 ` Dave Chinner 2020-04-08 17:09 ` Ira Weiny 2020-04-08 21:02 ` Dave Chinner 2020-04-08 21:28 ` Dan Williams 2020-04-08 22:10 ` Ira Weiny 2020-04-08 23:58 ` Dave Chinner 2020-04-09 0:22 ` Ira Weiny 2020-04-09 12:41 ` Christoph Hellwig 2020-04-09 20:49 ` Ira Weiny 2020-04-08 22:07 ` Ira Weiny 2020-04-08 23:21 ` Dave Chinner 2020-04-09 0:12 ` Ira Weiny 2020-04-09 0:30 ` Darrick J. Wong 2020-04-09 15:29 ` Ira Weiny 2020-04-09 16:59 ` Darrick J. Wong 2020-04-09 17:17 ` Jan Kara 2020-04-09 20:54 ` Ira Weiny 2020-04-09 0:49 ` Dave Chinner 2020-04-09 12:40 ` Christoph Hellwig 2020-04-10 0:27 ` Dave Chinner 2020-04-07 18:29 ` [PATCH V6 7/8] fs/xfs: Change xfs_ioctl_setattr_dax_invalidate() to xfs_ioctl_dax_check() ira.weiny 2020-04-08 2:23 ` Dave Chinner 2020-04-08 9:58 ` Jan Kara 2020-04-08 21:09 ` Dave Chinner 2020-04-08 22:26 ` Ira Weiny [this message] 2020-04-08 23:48 ` Dave Chinner 2020-04-09 12:28 ` Christoph Hellwig 2020-04-08 15:37 ` Darrick J. Wong 2020-04-08 18:13 ` Ira Weiny 2020-04-16 5:39 ` [fs/xfs] 857c9841f8: xfstests.xfs.046.fail kernel test robot 2020-04-07 18:29 ` [PATCH V6 8/8] Documentation/dax: Update Usage section ira.weiny
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