From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6F5CCC2BA1A for ; Wed, 8 Apr 2020 09:58:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5102420753 for ; Wed, 8 Apr 2020 09:58:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728056AbgDHJ6G (ORCPT ); Wed, 8 Apr 2020 05:58:06 -0400 Received: from mx2.suse.de ([195.135.220.15]:57678 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725932AbgDHJ6G (ORCPT ); Wed, 8 Apr 2020 05:58:06 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id DD924AC2C; Wed, 8 Apr 2020 09:58:03 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id B04B41E1239; Wed, 8 Apr 2020 11:58:03 +0200 (CEST) Date: Wed, 8 Apr 2020 11:58:03 +0200 From: Jan Kara To: Dave Chinner Cc: ira.weiny@intel.com, linux-kernel@vger.kernel.org, "Darrick J. Wong" , Dan Williams , Christoph Hellwig , "Theodore Y. Ts'o" , Jan Kara , Jeff Moyer , linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH V6 7/8] fs/xfs: Change xfs_ioctl_setattr_dax_invalidate() to xfs_ioctl_dax_check() Message-ID: <20200408095803.GB30172@quack2.suse.cz> References: <20200407182958.568475-1-ira.weiny@intel.com> <20200407182958.568475-8-ira.weiny@intel.com> <20200408022318.GJ24067@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200408022318.GJ24067@dread.disaster.area> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 08-04-20 12:23:18, Dave Chinner wrote: > On Tue, Apr 07, 2020 at 11:29:57AM -0700, ira.weiny@intel.com wrote: > > From: Ira Weiny > > > > 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 SUSE Labs, CR