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 Received: from lists.sourceforge.net (lists.sourceforge.net [216.105.38.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E6DE2CE79CF for ; Wed, 20 Sep 2023 11:57:09 +0000 (UTC) Received: from [127.0.0.1] (helo=sfs-ml-1.v29.lw.sourceforge.com) by sfs-ml-1.v29.lw.sourceforge.com with esmtp (Exim 4.95) (envelope-from ) id 1qivpM-0001zc-Iv; Wed, 20 Sep 2023 11:57:07 +0000 Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-1.v29.lw.sourceforge.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1qivpH-0001zO-HH for linux-f2fs-devel@lists.sourceforge.net; Wed, 20 Sep 2023 11:57:02 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sourceforge.net; s=x; h=MIME-Version:Content-Transfer-Encoding:Content-Type :References:In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=v+kxoG9eOGJ5xusIWXasOkiwnORCBCOMs4NdoCLCV+Y=; b=PEPUxsp9nNHKdlEmdhXvLhSQvn 8TNPkKhPreJLRqEsnNq1niBZwLLvRoM/gW39Q0P/HXKVQiZHzB1uz2kLdQ7gs9MuRXYNJFi05hX7f DCluYwFYWMAVvj+Mfa8MAsx7YFTOeyy/22dy6dMT1PpJZsnVeijWHGfra2BlLWgycG8w=; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sf.net; s=x ; h=MIME-Version:Content-Transfer-Encoding:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=v+kxoG9eOGJ5xusIWXasOkiwnORCBCOMs4NdoCLCV+Y=; b=A97EjphEm9hC9QC9hvMXLymb7+ HjoYgvsVO/KhjXTLoXQWGgGHFhYlN+KYJR5wtPhPt2fk3Q0Pdns15RdMqmgijAE8yQWZJsmwjgh1j QDEOqHC9+tQ2gm4I8g+xkFi57udzJnTveB4H4KfbnMztSbweCG8mY+Xond/GFTkRUKlo=; Received: from ams.source.kernel.org ([145.40.68.75]) by sfi-mx-1.v28.lw.sourceforge.com with esmtps (TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.95) id 1qivpF-00GdhQ-Dp for linux-f2fs-devel@lists.sourceforge.net; Wed, 20 Sep 2023 11:57:02 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 877BDB81BEB; Wed, 20 Sep 2023 11:56:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 677F3C433CD; Wed, 20 Sep 2023 11:56:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1695211011; bh=v+kxoG9eOGJ5xusIWXasOkiwnORCBCOMs4NdoCLCV+Y=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=Rg4SDYT2G/5iLIMjOccnvEi1JiFZ6DWISJeHQBkraG1wlEzFngIZ40YiKunM8cbSc +aGiW2BG1XlefCOYsICZDxSIj/cycJoqoVgH21scC+LvhZuM/I7QY33SH4s37GiB3i xx8VoYkq8098drZ1/id4lmBEMu3eQVNXWTxAUaEp2MAhsi3wNH08SmNvjfcYqsJCu1 KXrrrvTysK40Yb4V8RFHdyvz2X1AZgX3gj24E21SykmhPZrGV8Spjbs29Y+Wz+E6KX beC0Mxqh0EOjy/WL/hLY5L03MPDQWMARcGn8Qnl4hdNKDEe2Is8D1IwBJNuuGtXBBF rmhEIbbPeuCGA== Message-ID: <35c28758a9cc28a276a6b4b4ae8a420a1444e711.camel@kernel.org> From: Jeff Layton To: Christian Brauner Date: Wed, 20 Sep 2023 07:56:43 -0400 In-Reply-To: <20230920-raser-teehaus-029cafd5a6e4@brauner> References: <20230807-mgctime-v7-0-d1dec143a704@kernel.org> <20230919110457.7fnmzo4nqsi43yqq@quack3> <1f29102c09c60661758c5376018eac43f774c462.camel@kernel.org> <4511209.uG2h0Jr0uP@nimes> <08b5c6fd3b08b87fa564bb562d89381dd4e05b6a.camel@kernel.org> <20230920-leerung-krokodil-52ec6cb44707@brauner> <20230920101731.ym6pahcvkl57guto@quack3> <317d84b1b909b6c6519a2406fcb302ce22dafa41.camel@kernel.org> <20230920-raser-teehaus-029cafd5a6e4@brauner> User-Agent: Evolution 3.48.4 (3.48.4-1.fc38) MIME-Version: 1.0 X-Headers-End: 1qivpF-00GdhQ-Dp Subject: Re: [f2fs-dev] [PATCH v7 12/13] ext4: switch to multigrain timestamps X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Latchesar Ionkov , Martin Brandenburg , Konstantin Komarov , Jan Kara , linux-xfs@vger.kernel.org, "Darrick J. Wong" , Dominique Martinet , Christian Schoenebeck , linux-unionfs@vger.kernel.org, David Howells , Chris Mason , Andreas Dilger , Hans de Goede , Marc Dionne , codalist@coda.cs.cmu.edu, linux-afs@lists.infradead.org, linux-mtd@lists.infradead.org, Mike Marshall , Paulo Alcantara , Amir Goldstein , Eric Van Hensbergen , bug-gnulib@gnu.org, Andreas Gruenbacher , Miklos Szeredi , Richard Weinberger , Mark Fasheh , Hugh Dickins , Benjamin Coddington , Tyler Hicks , cluster-devel@redhat.com, coda@cs.cmu.edu, linux-mm@kvack.org, Gao Xiang , Iurii Zaikin , Namjae Jeon , Trond Myklebust , Xi Ruoyao , Shyam Prasad N , ecryptfs@vger.kernel.org, Kees Cook , ocfs2-devel@lists.linux.dev, linux-cifs@vger.kernel.org, linux-erofs@lists.ozlabs.org, Josef Bacik , Tom Talpey , Tejun Heo , Yue Hu , Alexander Viro , Ronnie Sahlberg , David Sterba , Jaegeuk Kim , ceph-devel@vger.kernel.org, Xiubo Li , Ilya Dryomov , OGAWA Hirofumi , Jan Harkes , linux-nfs@vger.kernel.org, linux-ext4@vger.kernel.org, Theodore Ts'o , Joseph Qi , Greg Kroah-Hartman , v9fs@lists.linux.dev, ntfs3@lists.linux.dev, samba-technical@lists.samba.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Steve French , Sergey Senozhatsky , Luis Chamberlain , Jeffle Xu , devel@lists.orangefs.org, Anna Schumaker , Jan Kara , Bo b Peterson , linux-fsdevel@vger.kernel.org, Andrew Morton , Sungjong Seo , Bruno Haible , linux-btrfs@vger.kernel.org, Joel Becker Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Wed, 2023-09-20 at 13:48 +0200, Christian Brauner wrote: > > > > While we initially thought we can do this unconditionally it turns out > > > > that this might break existing workloads that rely on timestamps in very > > > > specific ways and we always knew this was a possibility. Move > > > > multi-grain timestamps behind a vfs mount option. > > > > > > Surely this is a safe choice as it moves the responsibility to the sysadmin > > > and the cases where finegrained timestamps are required. But I kind of > > > wonder how is the sysadmin going to decide whether mgtime is safe for his > > > system or not? Because the possible breakage needn't be obvious at the > > > first sight... > > > > > > > That's the main reason I really didn't want to go with a mount option. > > Documenting that may be difficult. While there is some pessimism around > > it, I may still take a stab at just advancing the coarse clock whenever > > we fetch a fine-grained timestamp. It'd be nice to remove this option in > > the future if that turns out to be feasible. > > > > > If I were a sysadmin, I'd rather opt for something like > > > finegrained timestamps + lazytime (if I needed the finegrained timestamps > > > functionality). That should avoid the IO overhead of finegrained timestamps > > > as well and I'd know I can have problems with timestamps only after a > > > system crash. > > > > > I've just got another idea how we could solve the problem: Couldn't we > > > always just report coarsegrained timestamp to userspace and provide access > > > to finegrained value only to NFS which should know what it's doing? > > > > > > > I think that'd be hard. First of all, where would we store the second > > timestamp? We can't just truncate the fine-grained ones to come up with > > a coarse-grained one. It might also be confusing having nfsd and local > > filesystems present different attributes. > > As far as I can tell we have two options. The first one is to make this > into a mount option which I really think isn't a big deal and lets us > avoid this whole problem while allowing filesytems exposed via NFS to > make use of this feature for change tracking. > > The second option is that we turn off fine-grained finestamps for v6.6 > and you get to explore other options. > > It isn't a big deal regressions like this were always to be expected but > v6.6 needs to stabilize so anything that requires more significant work > is not an option. Oh, absolutely. I wasn't proposing to do that work for v6.6. For that, we absolutely either need the mount option or to just revert the mgtime conversions. My plan was to take a stab at doing this for a later kernel release. This is very much a "back to the drawing board" idea. It may not pan out after all, but if it does then we could consider removing the mount option at that point. -- Jeff Layton _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel