On Wed 08-04-20 12:23:18, Dave Chinner wrote: > On Tue, Apr 07, 2020 at 11:29:57AM -0700, ira.weiny@xxxxxxxxx wrote: > > From: Ira Weiny <ira.weiny@xxxxxxxxx> > > > > 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. 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 - because that often means you need to restart the application using the file anyway for the flag change to have any effect. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
