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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 C09C3C2BA19 for ; Tue, 21 Apr 2020 23:16:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 999EB206D5 for ; Tue, 21 Apr 2020 23:16:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726224AbgDUXQM (ORCPT ); Tue, 21 Apr 2020 19:16:12 -0400 Received: from outgoing-auth-1.mit.edu ([18.9.28.11]:57798 "EHLO outgoing.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726039AbgDUXQL (ORCPT ); Tue, 21 Apr 2020 19:16:11 -0400 Received: from callcc.thunk.org (pool-100-0-195-244.bstnma.fios.verizon.net [100.0.195.244]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id 03LNFr6S004708 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 21 Apr 2020 19:15:54 -0400 Received: by callcc.thunk.org (Postfix, from userid 15806) id 78DCE42030C; Tue, 21 Apr 2020 19:15:53 -0400 (EDT) Date: Tue, 21 Apr 2020 19:15:53 -0400 From: "Theodore Y. Ts'o" To: Christoph Hellwig Cc: Jan Kara , Dave Chinner , Ritesh Harjani , bugzilla-daemon@bugzilla.kernel.org, linux-ext4@vger.kernel.org, "Darrick J. Wong" , linux-fsdevel@vger.kernel.org Subject: Re: [Bug 207367] Accraid / aptec / Microsemi / ext4 / larger then 16TB Message-ID: <20200421231553.GB4278@mit.edu> References: <20200421042039.BF8074C046@d06av22.portsmouth.uk.ibm.com> <20200421050850.GB27860@dread.disaster.area> <20200421080405.GA4149@infradead.org> <20200421162910.GB5118@quack2.suse.cz> <20200421164554.GA3271@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200421164554.GA3271@infradead.org> Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Tue, Apr 21, 2020 at 09:45:54AM -0700, Christoph Hellwig wrote: > On Tue, Apr 21, 2020 at 06:29:10PM +0200, Jan Kara wrote: > > Well, there are two problems with this - firstly, ocfs2 is also using jbd2 > > and it knows nothing about iomap. So that would have to be implemented. > > Secondly, you have to somehow pass iomap ops to jbd2 so it all boils down > > to passing some callback to jbd2 during journal init to map blocks anyway > > as Dave said. And then it is upto filesystem to do the mapping - usually > > directly using its internal block mapping function - so no need for iomap > > AFAICT. > > You'll need to describe the mapping some how. So why not reuse an > existing mechanism instead of creating a new ad-hoc one? Well, we could argue that bmap() is an "existing mechanism" --- again, bmap() returns a u64, so it's perfectly fine. It's FIBMAP which is "fundamentally broken", not bmap(). If the goal is to eventually eliminate bmap() and aops->bmap(), sure, then we should force march all file systems to use iomap_bmap(), including ocfs2. Otherwise, if the goal alert users of FIBMAP when it's returning an corrutped block number, why not move the check if the block is larger than INT_MAX to ioctl_fibmap() in fs/ioctl.c, instead of in iomap_bmap()? If we can't fix this, I'm beginning to think that switching to iomap for fiemap and bmap is actually a lose for ext4. It's causing performance regressions, and now we see it's causing functionality regressions. Sure, it's saving a bit of code size, but is it really worth it to use iomap for fiemap/bmap? - Ted