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 39ABACE79A9 for ; Tue, 19 Sep 2023 20:46:45 +0000 (UTC) Received: from [127.0.0.1] (helo=sfs-ml-4.v29.lw.sourceforge.com) by sfs-ml-4.v29.lw.sourceforge.com with esmtp (Exim 4.95) (envelope-from ) id 1qihcI-0000lT-9L; Tue, 19 Sep 2023 20:46:42 +0000 Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-4.v29.lw.sourceforge.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1qihcG-0000lN-Vo for linux-f2fs-devel@lists.sourceforge.net; Tue, 19 Sep 2023 20:46:41 +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=Oq9r5r2xAoTCHNL1vl2zSAFYfwjFL747s/IzDVzwbJQ=; b=JBeMYWgcwDZzUjDM9bo13P/1xu Eu7uzPzKyPPkQOFOlASOn5NF+rtuUGuvMB4yKWKgocxAaUyZEo8Cg+tFr2v4HVkeWyk091gFt8UBt a2bVsk27A//a3diPrXCUcJCR+Tlaz9hCwW7Vr3WcBngQATNGoAg6WPLAlxzbwjw9Onus=; 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=Oq9r5r2xAoTCHNL1vl2zSAFYfwjFL747s/IzDVzwbJQ=; b=ZqRtADdnpLQzoeeNw7F1aqWST4 kNR1eCwUkCcviE8JsasxfRD7Z6gEMOMKTWXbXfH+hvnrgvsODTBz7RJWFVwYcE3NU1rRU6tM65W6u qbn9hObZea1l7lphzpJTS2q0Otfk9B2v5plXg9MCoJJ4D74Kw/j7dazp0o0Hr/s/Y3AM=; Received: from dfw.source.kernel.org ([139.178.84.217]) by sfi-mx-1.v28.lw.sourceforge.com with esmtps (TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.95) id 1qihcF-00FORY-Nm for linux-f2fs-devel@lists.sourceforge.net; Tue, 19 Sep 2023 20:46:41 +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 dfw.source.kernel.org (Postfix) with ESMTPS id F2E59617B9; Tue, 19 Sep 2023 20:46:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A819FC433C9; Tue, 19 Sep 2023 20:46:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1695156393; bh=BmRXQZIEgC13FrkspW8zNhSJjLbclay0bgLqEV3Rrl8=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=q9KdgZu946MZfw7DxJLZIxiiIbHL9p62pycuILxZHzw8MqP3sd2qzr3E/ZkzfhbEv Sv560WUNQE0HlwP/5rEqpm3bw7jCmrV5akvxgau1zBqN4rLOK+/ZjoboBONeleNI+5 6SP6lExUu15oD0xQisxQolfz9bgwYx59X/D7X0LTGvi5p2a+XVoY+oMnByTr4quQRa dZXyYP7t6FAFej2yuwhu+Ce8pxPjyRxtNPk1CXlFaDLgBYYr9H9mjHCggTcasxMD+A UZV+ik47sNRSAwVomJhe40/Ndx/tHAngLhTIM40zYtZFnzpPzdTJ314IhHsCYJFhNI PFuADp6gLFx9g== Message-ID: <6e6da8a875a0defec1a0f58314995a6a12dca74e.camel@kernel.org> From: Jeff Layton To: Paul Eggert , Bruno Haible , Jan Kara , Xi Ruoyao , bug-gnulib@gnu.org Date: Tue, 19 Sep 2023 16:46:25 -0400 In-Reply-To: References: <20230807-mgctime-v7-0-d1dec143a704@kernel.org> <20230919110457.7fnmzo4nqsi43yqq@quack3> <1f29102c09c60661758c5376018eac43f774c462.camel@kernel.org> <4511209.uG2h0Jr0uP@nimes> <08b5c6fd3b08b87fa564bb562d89381dd4e05b6a.camel@kernel.org> User-Agent: Evolution 3.48.4 (3.48.4-1.fc38) MIME-Version: 1.0 X-Headers-End: 1qihcF-00FORY-Nm 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 13:10 -0700, Paul Eggert wrote: > On 2023-09-19 09:31, Jeff Layton wrote: > > 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? > > I vaguely remember running into problems with 'make' a while ago > (perhaps with a BSDish system) when filesystem timestamps were > arbitrarily truncated in some cases but not others. These files would > look older than they really were, so 'make' would think they were > up-to-date when they weren't, and 'make' would omit actions that it > should have done, thus screwing up the build. > > File timestamps can be close together with 'make -j' on fast hosts. > Sometimes a shell script (or 'make' itself) will run 'make', then modify > a file F, then immediately run 'make' again; the latter 'make' won't > work if F's timestamp is mistakenly older than targets that depend on it. > > Although 'make'-like apps are the biggest canaries in this coal mine, > the issue also affects 'find -newer' (as Bruno mentioned), 'rsync -u', > 'mv -u', 'tar -u', Emacs file-newer-than-file-p, and surely many other > places. For example, any app that creates a timestamp file, then backs > up all files newer than that file, would be at risk. > > > > 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? > > Wouldn't this need to be done globally, that is, not just on a per-file > or per-filesystem basis? If so, I don't see how we'd avoid locking > performance issues. > Maybe. Another idea might be to introduce a new timekeeper for multigrain filesystems, but all of those would likely have to share the same coarse-grained clock source. So yeah, if you stat an inode and then update it, any inode written on a multigrain filesystem within the same jiffy-sized window would have to log an extra transaction to write out the inode. That's what I meant when I was talking about write amplification. > > PS. Although I'm no expert in the Linux inode code I hope you don't mind > my asking a question about this part of inode_set_ctime_current: > > /* > * If we've recently updated with a fine-grained timestamp, > * then the coarse-grained one may still be earlier than the > * existing ctime. Just keep the existing value if so. > */ > ctime.tv_sec = inode->__i_ctime.tv_sec; > if (timespec64_compare(&ctime, &now) > 0) > return ctime; > > Suppose root used clock_settime to set the clock backwards. Won't this > code incorrectly refuse to update the file's timestamp afterwards? That > is, shouldn't the last line be "goto fine_grained;" rather than "return > ctime;", with the comment changed from "keep the existing value" to "use > a fine-grained value"? It is a problem, and Linus pointed that out yesterday, which is why I sent this earlier today: https://lore.kernel.org/linux-fsdevel/20230919-ctime-v1-1-97b3da92f504@kernel.org/T/#u Bear in mind that we're not dealing with a situation where the value has not been queried since its last update, so we don't need to use a fine grained timestamp there (and really, it's preferable not to do so). A coarse one should be fine in this case. -- Jeff Layton _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel