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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 AB3F7C433E0 for ; Fri, 19 Jun 2020 22:28:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83D74222E8 for ; Fri, 19 Jun 2020 22:28:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=fieldses.org header.i=@fieldses.org header.b="TxHnuQrC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729380AbgFSW2o (ORCPT ); Fri, 19 Jun 2020 18:28:44 -0400 Received: from fieldses.org ([173.255.197.46]:36586 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729364AbgFSW2o (ORCPT ); Fri, 19 Jun 2020 18:28:44 -0400 Received: by fieldses.org (Postfix, from userid 2815) id A5CCB9238; Fri, 19 Jun 2020 18:28:43 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.11.0 fieldses.org A5CCB9238 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fieldses.org; s=default; t=1592605723; bh=pnhuMgvSD1GD/tZdHnDUyuziixDCqg7yWc0/+nh60VA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TxHnuQrCOr95EL7w2sUwzbD+FLGVeqS1nmjw43M/NpxPXiP8j0rsV1OtRLdQnM9Dy O4/OZ0pFeXnzcMDFuCefnp4nI88RM3j7wy7rUmPc+2yLKavISC3mL+a27tdNPM+7tA XBPkSBUVaT+L4zZN4PLxlnRevdfgcSHwPIX6gRK0= Date: Fri, 19 Jun 2020 18:28:43 -0400 From: "J. Bruce Fields" To: Dave Chinner Cc: Masayoshi Mizuma , Eric Sandeen , "Darrick J. Wong" , Christoph Hellwig , Theodore Ts'o , Andreas Dilger , Alexander Viro , Masayoshi Mizuma , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs , jlayton@redhat.com Subject: Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts Message-ID: <20200619222843.GB2650@fieldses.org> References: <4cbb5cbe-feb4-2166-0634-29041a41a8dc@sandeen.net> <20200617184507.GB18315@fieldses.org> <20200618013026.ewnhvf64nb62k2yx@gabell> <20200618030539.GH2005@dread.disaster.area> <20200618034535.h5ho7pd4eilpbj3f@gabell> <20200618223948.GI2005@dread.disaster.area> <20200619022005.GA25414@fieldses.org> <20200619024455.GN2005@dread.disaster.area> <20200619204033.GB1564@fieldses.org> <20200619221044.GO2005@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200619221044.GO2005@dread.disaster.area> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Sat, Jun 20, 2020 at 08:10:44AM +1000, Dave Chinner wrote: > On Fri, Jun 19, 2020 at 04:40:33PM -0400, J. Bruce Fields wrote: > > On Fri, Jun 19, 2020 at 12:44:55PM +1000, Dave Chinner wrote: > > > On Thu, Jun 18, 2020 at 10:20:05PM -0400, J. Bruce Fields wrote: > > > > My memory was that after Jeff Layton's i_version patches, there wasn't > > > > really a significant performance hit any more, so the ability to turn it > > > > off is no longer useful. > > > > > > Yes, I completely agree with you here. However, with some > > > filesystems allowing it to be turned off, we can't just wave our > > > hands and force enable the option. Those filesystems - if the > > > maintainers chose to always enable iversion - will have to go > > > through a mount option deprecation period before permanently > > > enabling it. > > > > I don't understand why. > > > > The filesystem can continue to let people set iversion or noiversion as > > they like, while under the covers behaving as if iversion is always set. > > I can't see how that would break any application. (Or even how an > > application would be able to detect that the filesystem was doing this.) > > It doesn't break functionality, but it affects performance. I thought you just agreed above that any performance hit was not "significant". > IOWs, it can make certain workloads go a lot slower in some > circumstances. And that can result in unexectedly breaking SLAs or > slow down a complex, finely tuned data center wide workload to the > point it no longer meets requirements. Such changes in behaviour are > considered a regression, especially if they result from a change that > just ignores the mount option that turned off that specific feature. I get that, but, what's the threshhold here for a significant risk of regression? The "noiversion" behavior is kinda painful for NFS. --b.