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 1EFC6CE79A9 for ; Tue, 19 Sep 2023 16:31:36 +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 1qiddO-00035L-LH; Tue, 19 Sep 2023 16:31:33 +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 1qiddK-00035F-Qq for linux-f2fs-devel@lists.sourceforge.net; Tue, 19 Sep 2023 16:31:29 +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=2YOWI6/JAFOB4t8+Jl1G0UAU2WJNOEKR+ozWrF+wCHw=; b=PYmTSnkepDcDHu4yJ8dG+TRJ7p fgCqe8QT9DtnZk12nkmzkJNikU4bLgBxy7epTQWrYdtfUwErFygur61+pw5LjKm4WWD6DNn1Se6SL 3uOtHDyGWCR8Sl0czSamQ+iJdtrdreh39HJIj7ETyp91Rw5BoV27zDE4zBFo1xywBsQk=; 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=2YOWI6/JAFOB4t8+Jl1G0UAU2WJNOEKR+ozWrF+wCHw=; b=WPJDHhmZZIUmw9arxx7GiGU3U7 vszI8b+suOPF3D8neVuRtT/UkhUOuS8FnvqrnjwHAC3bQF+rH96N4CKV20PFkC3chTeoOQ60j7iCo EYZKZatgzDix/rjQji8diU4OUn/lKDqq71pR3Wxuof/qF8H2AE7Dr1K3l0CFkJDoxxFc=; Received: from sin.source.kernel.org ([145.40.73.55]) by sfi-mx-2.v28.lw.sourceforge.com with esmtps (TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.95) id 1qiddI-0007pT-F4 for linux-f2fs-devel@lists.sourceforge.net; Tue, 19 Sep 2023 16:31:29 +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 sin.source.kernel.org (Postfix) with ESMTPS id 8CD0BCE139A; Tue, 19 Sep 2023 16:31:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 07A27C433CD; Tue, 19 Sep 2023 16:31:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1695141076; bh=2YOWI6/JAFOB4t8+Jl1G0UAU2WJNOEKR+ozWrF+wCHw=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=NSgO9mQ/kogScKOyruXs27QKGb28KeH5iN8518jdQIxYZ9Zq8W5Yeb8HJpLNbIZ40 EQDdGtIWCMRwCZr+hkVhSKagEDB2fBTdAzDnNexBTyvRGH8+mWpGC7k4O3oOthSODy kLPJh5RYmd+l51ixbejRXP63ZyU1UyglaFGETEGRw2BGftvafb/kUzhWZeRY/B1ibo Wti21rW2JgdQmcow8/EHQlT7uWQR0pPH/ecD4lkrfORAvjqUH6xcDxBDFUTwISNY24 GBmtqEOt9wCW1B2y4/2rn4A5SVB2ofaAjm8Z64p+ka1gu4ZTZ9u3KdunqSf9K8+AlP OJGP0iADrktsQ== Message-ID: <08b5c6fd3b08b87fa564bb562d89381dd4e05b6a.camel@kernel.org> From: Jeff Layton To: Bruno Haible , Jan Kara , Xi Ruoyao , bug-gnulib@gnu.org Date: Tue, 19 Sep 2023 12:31:08 -0400 In-Reply-To: <4511209.uG2h0Jr0uP@nimes> References: <20230807-mgctime-v7-0-d1dec143a704@kernel.org> <20230919110457.7fnmzo4nqsi43yqq@quack3> <1f29102c09c60661758c5376018eac43f774c462.camel@kernel.org> <4511209.uG2h0Jr0uP@nimes> User-Agent: Evolution 3.48.4 (3.48.4-1.fc38) MIME-Version: 1.0 X-Headers-End: 1qiddI-0007pT-F4 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 , 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 , 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, Ilya Dryomov , Iurii Zaikin , Namjae Jeon , Trond Myklebust , Shyam Prasad N , ecryptfs@vger.kernel.org, Kees Cook , ocfs2-devel@lists.linux.dev, linux-cifs@vger.kernel.org, Josef Bacik , Tom Talpey , Tejun Heo , Yue Hu , Alexander Viro , Ronnie Sahlberg , David Sterba , Jaegeuk Kim , ceph-devel@vger.kernel.org, Xiubo Li , Gao Xiang , OGAWA Hirofumi , Jan Harkes , Christian Brauner , 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 , linux-erofs@lists.ozlabs.org, linux-nfs@vger.kernel.org, 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 Tue, 2023-09-19 at 16:52 +0200, Bruno Haible wrote: > Jeff Layton wrote: > > I'm not sure what we can do for this test. The nap() function is making > > an assumption that the timestamp granularity will be constant, and that > > isn't necessarily the case now. > > This is only of secondary importance, because the scenario by Jan Kara > shows a much more fundamental breakage: > > > > The ultimate problem is that a sequence like: > > > > > > write(f1) > > > stat(f2) > > > write(f2) > > > stat(f2) > > > write(f1) > > > stat(f1) > > > > > > can result in f1 timestamp to be (slightly) lower than the final f2 > > > timestamp because the second write to f1 didn't bother updating the > > > timestamp. That can indeed be a bit confusing to programs if they compare > > > timestamps between two files. Jeff? > > > > > > > Basically yes. > > f1 was last written to *after* f2 was last written to. If the timestamp of f1 > is then lower than the timestamp of f2, timestamps are fundamentally broken. > > Many things in user-space depend on timestamps, such as build system > centered around 'make', but also 'find ... -newer ...'. > What does breakage with make look like in this situation? The "fuzz" here is going to be on the order of a jiffy. The typical case for make timestamp comparisons is comparing source files vs. a build target. If those are being written nearly simultaneously, then that could be an issue, but is that a typical behavior? It seems like it would be hard to rely on that anyway, esp. given filesystems like NFS that can do lazy writeback. One of the operating principles with this series is that timestamps can be of varying granularity between different files. Note that Linux already violates this assumption when you're working across filesystems of different types. As to potential fixes if this is a real problem: I don't really want to put this behind a mount or mkfs option (a'la relatime, etc.), but that is one possibility. I wonder if it would be feasible to just advance the coarse-grained current_time whenever we end up updating a ctime with a fine-grained timestamp? It might produce some inode write amplification. Files that were written within the same jiffy could see more inode transactions logged, but that still might not be _too_ awful. I'll keep thinking about it for now. -- Jeff Layton _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel