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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 4BDCCC2BA19 for ; Thu, 23 Apr 2020 08:24:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2FECA208E4 for ; Thu, 23 Apr 2020 08:24:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726490AbgDWIY0 (ORCPT ); Thu, 23 Apr 2020 04:24:26 -0400 Received: from mx2.suse.de ([195.135.220.15]:60024 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725854AbgDWIYZ (ORCPT ); Thu, 23 Apr 2020 04:24:25 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 614CFAF79; Thu, 23 Apr 2020 08:24:23 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 731811E0E61; Thu, 23 Apr 2020 10:24:22 +0200 (CEST) Date: Thu, 23 Apr 2020 10:24:22 +0200 From: Jan Kara To: Ira Weiny Cc: "Darrick J. Wong" , linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, Dave Chinner , Jan Kara , Al Viro , Dan Williams , Dave Chinner , Christoph Hellwig , "Theodore Y. Ts'o" , Jeff Moyer , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH V9 03/11] fs/stat: Define DAX statx attribute Message-ID: <20200423082422.GA3737@quack2.suse.cz> References: <20200421191754.3372370-1-ira.weiny@intel.com> <20200421191754.3372370-4-ira.weiny@intel.com> <20200422162951.GE6733@magnolia> <20200422185121.GL3372712@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200422185121.GL3372712@iweiny-DESK2.sc.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 22-04-20 11:51:21, Ira Weiny wrote: > On Wed, Apr 22, 2020 at 09:29:51AM -0700, Darrick J. Wong wrote: > > On Tue, Apr 21, 2020 at 12:17:45PM -0700, ira.weiny@intel.com wrote: > > > From: Ira Weiny > > > > > > In order for users to determine if a file is currently operating in DAX > > > state (effective DAX). Define a statx attribute value and set that > > > attribute if the effective DAX flag is set. > > > > > > To go along with this we propose the following addition to the statx man > > > page: > > > > > > STATX_ATTR_DAX > > > > > > The file is in the DAX (cpu direct access) state. DAX state > > > 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 O_SYNC > > > where data and the necessary metadata are transferred together. > > > > > > A DAX file may support being mapped with the MAP_SYNC flag, > > > which enables a program to use CPU cache flush instructions to > > > persist CPU store operations without an explicit fsync(2). See > > > mmap(2) for more information. > > > > One thing I hadn't noticed before -- this is a change to userspace API, > > so please cc this series to linux-api@vger.kernel.org when you send V10. > > Right! Glad you caught me on this because I was just preparing to send V10. > > Is there someone I could directly mail who needs to look at this? I guess I > thought we had the important FS people involved for this type of API change. > :-/ I believe we have all the important people here. But linux-api is a general fallback list where people reviewing API changes linger. So when changing user facing API, it is good to CC this list. Honza -- Jan Kara SUSE Labs, CR