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=DKIM_SIGNED,DKIM_VALID, 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 12AF1C33CB1 for ; Thu, 16 Jan 2020 06:25:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D8F7920728 for ; Thu, 16 Jan 2020 06:25:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="u5kIlz7d" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730592AbgAPGZ5 (ORCPT ); Thu, 16 Jan 2020 01:25:57 -0500 Received: from mail-ot1-f65.google.com ([209.85.210.65]:35494 "EHLO mail-ot1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730302AbgAPGZx (ORCPT ); Thu, 16 Jan 2020 01:25:53 -0500 Received: by mail-ot1-f65.google.com with SMTP id i15so18408208oto.2 for ; Wed, 15 Jan 2020 22:25:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=0Q2Zze5PAbfGbIfzFdliXA62Y52BTomvMStI7KfWGBk=; b=u5kIlz7dq16rp2yrD78FB1VQ+w1Zq+JiSjBNilh5DRi9ac08AhhG0XDF9+gWsQ0qpy nPrmueWrxcoVKW2xQHkgjSCC/HAtaGq0F6o9mZiYIGXE2M+/oHKLChi/3SET+h2/jMge gdHRJFQskIPzuAAr2erbVkd1Vqf7B2Y9TpzL0K6Y09YJPlyumzeQ6+QXVQIqUZGH0KdP Ry+UfAL5nFVEdgiEYfWttB5EMFSnUtR7TlsE7HcXkBVw6yjtV1mebrsumkUQFFqveDNT BtjNugC2mm6DAp/slfvOUwzsk8q08hJISlAspgP1j4TZN69MyuzNRRaGYp0xWsEvnCkM XPig== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=0Q2Zze5PAbfGbIfzFdliXA62Y52BTomvMStI7KfWGBk=; b=pd5IDxbUnJ0MNKwvkC3fkzqXsHIjgzifXZ3IzSYZ0kVD4le3HnFbFL1cgH1KZZAzn2 pS4GxNDA2Z/7p9m3wgI7AQrNPBP0YNYKYOIpZesskmxZd8kIQXd/FVkVNf0Yl+uip9uR 1uSURe4CcoX+RijrYMCBvxGzddfKWJvO2+UsdeSgybowPQaBkpHlCJbQfEF9P2Odio5J xLrz5xFXmNOqMJARPgIZt3ihdpWurkmbiHjpWy8sLHn9+4dhIS9bqo7ESDJdgT+Fvq4e 25dQzgEHljYw5jjyHEUWIMDifdc1a16Bi9zSC5YQd5aJt7GOsw15g8HQbToBEC44f4dh tcBg== X-Gm-Message-State: APjAAAVsvkyBTZ/urNjLv64efnRpxz45Uq+bbqabdqvTgZWKXbshFTQS qyvNYVtCyEFe+obHHsp0EYn7nfpY5iyXOQUoFjt9iQ== X-Google-Smtp-Source: APXvYqwxrSywPSe+bSWTFb7guE1CCafYs03qvFymeop4ETyO8OyklXF9wh2bDlRNzFN+MYAZpycyHsRnLkWFEZhvIJE= X-Received: by 2002:a9d:6f11:: with SMTP id n17mr838191otq.126.1579155952021; Wed, 15 Jan 2020 22:25:52 -0800 (PST) MIME-Version: 1.0 References: <20200110192942.25021-1-ira.weiny@intel.com> <20200110192942.25021-2-ira.weiny@intel.com> <20200115113715.GB2595@quack2.suse.cz> <20200115173834.GD8247@magnolia> <20200115194512.GF23311@iweiny-DESK2.sc.intel.com> <20200115223821.GG23311@iweiny-DESK2.sc.intel.com> <20200116053935.GB8235@magnolia> <20200116061804.GI8257@magnolia> In-Reply-To: <20200116061804.GI8257@magnolia> From: Dan Williams Date: Wed, 15 Jan 2020 22:25:41 -0800 Message-ID: Subject: Re: [RFC PATCH V2 01/12] fs/stat: Define DAX statx attribute To: "Darrick J. Wong" Cc: Ira Weiny , Jan Kara , Linux Kernel Mailing List , Alexander Viro , Dave Chinner , Christoph Hellwig , "Theodore Y. Ts'o" , linux-ext4 , linux-xfs , linux-fsdevel Content-Type: text/plain; charset="UTF-8" Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Wed, Jan 15, 2020 at 10:18 PM Darrick J. Wong wrote: > > On Wed, Jan 15, 2020 at 10:05:00PM -0800, Dan Williams wrote: > > On Wed, Jan 15, 2020 at 9:39 PM Darrick J. Wong wrote: > > [..] > > > > attempts to minimize software cache effects for both I/O and > > > > memory mappings of this file. It requires a file system which > > > > has been configured to support DAX. > > > > > > > > DAX generally assumes all accesses are via cpu load / store > > > > instructions which can minimize overhead for small accesses, but > > > > may adversely affect cpu utilization for large transfers. > > > > > > > > File I/O is done directly to/from user-space buffers and memory > > > > mapped I/O may be performed with direct memory mappings that > > > > bypass kernel page cache. > > > > > > > > While the DAX property tends to result in data being transferred > > > > synchronously, it does not give the same guarantees of > > > > synchronous I/O where data and the necessary metadata are > > > > transferred together. > > > > > > (I'm frankly not sure that synchronous I/O actually guarantees that the > > > metadata has hit stable storage...) > > > > Oh? That text was motivated by the open(2) man page description of O_SYNC. > > Eh, that's just me being cynical about software. Yes, the O_SYNC docs > say that data+metadata are supposed to happen; that's good enough for > another section in the man pages. :) > Ah ok, yes, "all storage is a lie".