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 D952CC43331 for ; Fri, 3 Apr 2020 04:39:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AE327206F8 for ; Fri, 3 Apr 2020 04:39:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731546AbgDCEjD (ORCPT ); Fri, 3 Apr 2020 00:39:03 -0400 Received: from mga09.intel.com ([134.134.136.24]:19394 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725851AbgDCEjD (ORCPT ); Fri, 3 Apr 2020 00:39:03 -0400 IronPort-SDR: H/LQxK3d0Y3xA0ApWFa+6DRBQjdAJjbAP/3PQFZfUI66Od1mF+IgVnVaImVnpeV6ZV7EDcWrZI x+sksbogFKAw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Apr 2020 21:39:02 -0700 IronPort-SDR: xKrqCXM86SXhnugdFt3obxFXmfKoeWIC1M5kbMc+05JVG/0Gfn2PTYInne6x+V61j2AhVn+fUh 37/DnQQipmOA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,338,1580803200"; d="scan'208";a="241021226" Received: from iweiny-desk2.sc.intel.com ([10.3.52.147]) by fmsmga007.fm.intel.com with ESMTP; 02 Apr 2020 21:39:01 -0700 Date: Thu, 2 Apr 2020 21:39:01 -0700 From: Ira Weiny To: "Darrick J. Wong" Cc: Christoph Hellwig , Dave Chinner , "Theodore Y. Ts'o" , Dan Williams , Jan Kara , Linux Kernel Mailing List , Alexander Viro , linux-ext4 , linux-xfs , linux-fsdevel , Andrew Morton , Linus Torvalds Subject: Re: [PATCH V5 00/12] Enable per-file/per-directory DAX operations V5 Message-ID: <20200403043901.GH3952565@iweiny-DESK2.sc.intel.com> References: <20200227052442.22524-1-ira.weiny@intel.com> <20200305155144.GA5598@lst.de> <20200309170437.GA271052@iweiny-DESK2.sc.intel.com> <20200311033614.GQ1752567@magnolia> <20200311062952.GA11519@lst.de> <20200316095224.GF12783@quack2.suse.cz> <20200316095509.GA13788@lst.de> <20200401040021.GC56958@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200401040021.GC56958@magnolia> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 01, 2020 at 04:00:21AM +0000, Darrick J. Wong wrote: > On Mon, Mar 16, 2020 at 10:55:09AM +0100, Christoph Hellwig wrote: > > On Mon, Mar 16, 2020 at 10:52:24AM +0100, Jan Kara wrote: > > > > This sounds reasonable to me. > > > > > > > > As for deprecating the mount option, I think at a minimum it needs to > > > > continue be accepted as an option even if it is ignored to not break > > > > existing setups. > > > > > > Agreed. But that's how we usually deprecate mount options. Also I'd say > > > that statx() support for reporting DAX state and some education of > > > programmers using DAX is required before we deprecate the mount option > > > since currently applications check 'dax' mount option to determine how much > > > memory they need to set aside for page cache before they consume everything > > > else on the machine... > > > > I don't even think we should deprecate it. It isn't painful to maintain > > and actually useful for testing. Instead we should expand it into a > > tristate: > > > > dax=off > > dax=flag > > dax=always > > > > where the existing "dax" option maps to "dax=always" and nodax maps > > to "dax=off". and dax=flag becomes the default for DAX capable devices. > > That works for me. In summary: > > - Applications must call statx to discover the current S_DAX state. > > - There exists an advisory file inode flag FS_XFLAG_DAX that can be > changed on files that have no blocks allocated to them. Changing > this flag does not necessarily change the S_DAX state immediately > but programs can query the S_DAX state via statx. > > If FS_XFLAG_DAX is set and the fs is on pmem then it will always > enable S_DAX at inode load time; if FS_XFLAG_DAX is not set, it will > never enable S_DAX. Unless overridden... > > - There exists a dax= mount option. dax=off means "never set S_DAX, > ignore FS_XFLAG_DAX"; dax=always means "always set S_DAX (at least on > pmem), ignore FS_XFLAG_DAX"; and dax=iflag means "follow FS_XFLAG_DAX" > and is the default. "dax" by itself means "dax=always". "nodax" > means "dax=off". > > - There exists an advisory directory inode flag FS_XFLAG_DAX that can > be changed at any time. The flag state is copied into any files or > subdirectories created within that directory. If programs require > that file access runs in S_DAX mode, they'll have to create those > files themselves inside a directory with FS_XFLAG_DAX set, or mount > the fs with dax=always. One other thing to add here. They _can_ set the FS_XFLAG_DAX on a file with data and force an eviction to get S_DAX to change. I think that is a nice reason to have a different error code returned. > > Ok? Let's please get this part finished for 5.8, then we can get back > to arguing about fs-rmap and reflink and dax and whatnot. I'm happy to see you motivated to get this in. I'm starting with a new xfstest to make sure we agree on the semantics prior to more patches. I hope to have the xfstest patch sent tomorrow sometime. Ira > > --D