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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,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 AAEFEC43381 for ; Thu, 14 Mar 2019 09:06:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 82EBD2184E for ; Thu, 14 Mar 2019 09:06:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726539AbfCNJGh (ORCPT ); Thu, 14 Mar 2019 05:06:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:54422 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726284AbfCNJGh (ORCPT ); Thu, 14 Mar 2019 05:06:37 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id A2D92AEA3; Thu, 14 Mar 2019 09:06:35 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 49D8B1E3FE8; Thu, 14 Mar 2019 10:06:35 +0100 (CET) Date: Thu, 14 Mar 2019 10:06:35 +0100 From: Jan Kara To: Christopher Lameter Cc: Christoph Hellwig , Dave Chinner , Ira Weiny , john.hubbard@gmail.com, Andrew Morton , linux-mm@kvack.org, Al Viro , Christian Benvenuti , Dan Williams , Dennis Dalessandro , Doug Ledford , Jan Kara , Jason Gunthorpe , Jerome Glisse , Matthew Wilcox , Michal Hocko , Mike Rapoport , Mike Marciniszyn , Ralph Campbell , Tom Talpey , LKML , linux-fsdevel@vger.kernel.org, John Hubbard Subject: Re: [PATCH v3 0/1] mm: introduce put_user_page*(), placeholder versions Message-ID: <20190314090635.GC16658@quack2.suse.cz> References: <20190306235455.26348-1-jhubbard@nvidia.com> <010001695b4631cd-f4b8fcbf-a760-4267-afce-fb7969e3ff87-000000@email.amazonses.com> <20190310224742.GK26298@dastard> <01000169705aecf0-76f2b83d-ac18-4872-9421-b4b6efe19fc7-000000@email.amazonses.com> <20190312103932.GD1119@iweiny-DESK2.sc.intel.com> <20190312221113.GF23020@dastard> <20190313160319.GA15134@infradead.org> <010001697880bfdc-4503d0dd-03cd-4c91-84a0-c18af1eab145-000000@email.amazonses.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <010001697880bfdc-4503d0dd-03cd-4c91-84a0-c18af1eab145-000000@email.amazonses.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed 13-03-19 19:21:37, Christopher Lameter wrote: > On Wed, 13 Mar 2019, Christoph Hellwig wrote: > > > On Wed, Mar 13, 2019 at 09:11:13AM +1100, Dave Chinner wrote: > > > On Tue, Mar 12, 2019 at 03:39:33AM -0700, Ira Weiny wrote: > > > > IMHO I don't think that the copy_file_range() is going to carry us through the > > > > next wave of user performance requirements. RDMA, while the first, is not the > > > > only technology which is looking to have direct access to files. XDP is > > > > another.[1] > > > > > > Sure, all I doing here was demonstrating that people have been > > > trying to get local direct access to file mappings to DMA directly > > > into them for a long time. Direct Io games like these are now > > > largely unnecessary because we now have much better APIs to do > > > zero-copy data transfer between files (which can do hardware offload > > > if it is available!). > > > > And that is just the file to file case. There are tons of other > > users of get_user_pages, including various drivers that do large > > amounts of I/O like video capture. For them it makes tons of sense > > to transfer directly to/from a mmap()ed file. > > That is very similar to the RDMA case and DAX etc. We need to have a way > to tell a filesystem that this is going to happen and that things need to > be setup for this to work properly. The way to tell filesystem what's happening is exactly what we are working on with these patches... > But if that has not been done then I think its proper to fail a long term > pin operation on page cache pages. Meaning the regular filesystems > maintain control of whats happening with their pages. And as I mentioned in my other email, we cannot just fail the pin for pagecache pages as that would regress existing applications. Honza -- Jan Kara SUSE Labs, CR