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=ham 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 84E51C04EB8 for ; Sat, 8 Dec 2018 18:13:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 41A832054F for ; Sat, 8 Dec 2018 18:13:13 +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="BBW4Oyv+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 41A832054F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726224AbeLHSNM (ORCPT ); Sat, 8 Dec 2018 13:13:12 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:48162 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726142AbeLHSNL (ORCPT ); Sat, 8 Dec 2018 13:13:11 -0500 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=xJEBp/3asiHVeZps7v/zV1QboJYOn6XLUjrWKYUW3XE=; b=BBW4Oyv+pinFAiV/fYKMbsdlv vCGwnzOHMuWRTFHYh8EgYfkACZoJx0cvPifMz7AZPa6tSTl02gvzyCDQzcHhLU6Gpaf1K/TngOUVC 1N946RqCYEUAatBvDuBzRqOBOshBQB+v28xnYBcTIpmpiTHSPm7VCyPNZC9W65CAde8XJ2Fpq00bt e0iBmhuCjuUvYQN+AGPrt9+cBzfTMFpB/WAP2qgSK+wivjv/FRBx2RV0nR7ANEPzGfZOZH2MV8BXU hmU+Q8moa7QUpSoFs512IMObs9PpRr4f05p7yRiP23xCCRQYyj0UxotFIzhWiY8SgXvNO7KrwQr/h 5UYP0D2Cg==; Received: from hch by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1gVh63-0003Pd-2C; Sat, 08 Dec 2018 18:12:59 +0000 Date: Sat, 8 Dec 2018 10:12:58 -0800 From: Christoph Hellwig To: Dan Williams Cc: Christoph Hellwig , =?iso-8859-1?B?Suly9G1l?= Glisse , John Hubbard , Matthew Wilcox , John Hubbard , Andrew Morton , Linux MM , Jan Kara , tom@talpey.com, Al Viro , benve@cisco.com, Christopher Lameter , "Dalessandro, Dennis" , Doug Ledford , Jason Gunthorpe , Michal Hocko , Mike Marciniszyn , rcampbell@nvidia.com, Linux Kernel Mailing List , linux-fsdevel Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions Message-ID: <20181208181258.GA13075@infradead.org> References: <20181205011519.GV10377@bombadil.infradead.org> <20181205014441.GA3045@redhat.com> <59ca5c4b-fd5b-1fc6-f891-c7986d91908e@nvidia.com> <7b4733be-13d3-c790-ff1b-ac51b505e9a6@nvidia.com> <20181207191620.GD3293@redhat.com> <3c4d46c0-aced-f96f-1bf3-725d02f11b60@nvidia.com> <20181208163353.GA2952@redhat.com> <20181208164825.GA26154@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Dec 08, 2018 at 10:09:26AM -0800, Dan Williams wrote: > Another fix that may put pressure 'struct page' is resolving the > untenable situation of dax being incompatible with reflink, i.e. > reflink currently requires page-cache pages. Dave has talked about > silently establishing page-cache entries when a dax-page is cow'd for > reflink, but I wonder if we could go the other way and introduce the > mechanism of a page belonging to multiple mappings simultaneously and > managed by the filesystem. FYI, I had a a prototype for DAX + reflink that didn't require the page cache, although it badly reimplemented parts of it. But that was a long time ago, before we started requiring struct page for the DAX memory.