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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable 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 2AC67C43219 for ; Thu, 2 May 2019 01:52:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ED5AC206DF for ; Thu, 2 May 2019 01:52:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="e1Cdnr7M" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726194AbfEBBwR (ORCPT ); Wed, 1 May 2019 21:52:17 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:44398 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726152AbfEBBwR (ORCPT ); Wed, 1 May 2019 21:52:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding: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=xNjOP9gg2QMy4x3ICBZoOoeoO4NbjsoS8XWQ33F0y5I=; b=e1Cdnr7Mt+nZArvTOHcIt/dcH Ie+TXMWhFAYA5HNxT+y63lHRcgthMLNLL/PSs84r2uhvCLp73HMv7fZ+6i58oeYNTdQzpVsYqdBF3 nSsIM/r501mqjtAIkshkaSAWXLi3+lfbyh811CpB3RgxxHaVYJa6loRHloXhQ1iJ/dbbmb3AJHj1t pj+KBXXwUGZS7zTl5dGTlNJJTY1q4Id6eY+DUeLIZg2fShSdrsNHDR9dS/jmOXHnDsJZoKQLz3Qn1 j4DV7gXZmiWBaXasQ1mnVROZhkNd7/lbqMTeCiyj5EpOonGLtzfwRwoMya+eznp6sO5aOwOgMiYnW PWVOs2XIQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1hM0tT-0005DI-4W; Thu, 02 May 2019 01:52:15 +0000 Date: Wed, 1 May 2019 18:52:14 -0700 From: Matthew Wilcox To: Jerome Glisse Cc: Dave Chinner , lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [LSF/MM TOPIC] Direct block mapping through fs for device Message-ID: <20190502015214.GB8099@bombadil.infradead.org> References: <20190426013814.GB3350@redhat.com> <20190426062816.GG1454@dread.disaster.area> <20190426152044.GB13360@redhat.com> <20190427012516.GH1454@dread.disaster.area> <20190429132643.GB3036@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190429132643.GB3036@redhat.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Apr 29, 2019 at 09:26:45AM -0400, Jerome Glisse wrote: > This is a filesystem opt-in feature if a given filesystem do not want > to implement it then just do not implement it and it will use page > cache. It is not mandatory i am not forcing anyone. The first reasons > for those are not filesystem but mmap of device file. But as LSF/MM > is up i thought it would be a good time to maybe propose that for file- > system too. If you do not want that for your filesystem then just NAK > any patch that add that to filesystem you care about. No. This is stupid, broken, and wrong. I know we already have application-visible differences between filesystems, and every single one of those is a bug. They may be hard bugs to fix, they may be bugs that we feel like we can't fix, they may never be fixed. But they are all bugs. Applications should be able to work on any Linux filesystem without having to care what it is. Code has a tendency to far outlive its authors expectations (and indeed sometimes its authors). If 'tar' had an #ifdef XFS / #elsif EXT4 / #elsif BTRFS / ... #endif, that would be awful. We need the same semantics across all major filesystems. Anything else is us making application developers lives harder than necessary, and that's unacceptable.