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=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 36A41C282D7 for ; Tue, 5 Feb 2019 18:01:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 001F32184B for ; Tue, 5 Feb 2019 18:01:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728513AbfBESBl (ORCPT ); Tue, 5 Feb 2019 13:01:41 -0500 Received: from mga09.intel.com ([134.134.136.24]:42041 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726534AbfBESBk (ORCPT ); Tue, 5 Feb 2019 13:01:40 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 05 Feb 2019 10:01:40 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,336,1544515200"; d="scan'208";a="124180424" Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by orsmga003.jf.intel.com with ESMTP; 05 Feb 2019 10:01:39 -0800 Date: Tue, 5 Feb 2019 10:01:20 -0800 From: Ira Weiny To: lsf-pc@lists.linux-foundation.org, linux-rdma@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: John Hubbard , Jan Kara , Jerome Glisse , Dan Williams , Matthew Wilcox , Dave Chinner , Doug Ledford , Michal Hocko , Jason Gunthorpe Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA Message-ID: <20190205180120.GC21617@iweiny-DESK2.sc.intel.com> References: <20190205175059.GB21617@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190205175059.GB21617@iweiny-DESK2.sc.intel.com> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I had an old invalid address for Jason Gunthorpe in my address book... Correcting his email in the thread. On Tue, Feb 05, 2019 at 09:50:59AM -0800, 'Ira Weiny' wrote: > > The problem: Once we have pages marked as GUP-pinned how should various > subsystems work with those markings. > > The current work for John Hubbards proposed solutions (part 1 and 2) is > progressing.[1] But the final part (3) of his solution is also going to take > some work. > > In Johns presentation he lists 3 alternatives for gup-pinned pages: > > 1) Hold off try_to_unmap > 2) Allow writeback while pinned (via bounce buffers) > [Note this will not work for DAX] > 3) Use a "revocable reservation" (or lease) on those pages > 4) Pin the blocks as busy in the FS allocator > > The problem with lease's on pages used by RDMA is that the references to > these pages is not local to the machine. Once the user has been given access > to the page they, through the use of a remote tokens, give a reference to that > page to remote nodes. This is the core essence of RDMA, and like it or not, > something which is increasingly used by major Linux users. > > Therefore we need to discuss the extent by which leases are appropriate and > what happens should a lease be revoked which a user does not respond to. > > As John Hubbard put it: > > "Other filesystem features that need to replace the page with a new one can > be inhibited for pages that are GUP-pinned. This will, however, alter and > limit some of those filesystem features. The only fix for that would be to > require GUP users monitor and respond to CPU page table updates. Subsystems > such as ODP and HMM do this, for example. This aspect of the problem is > still under discussion." > > -- John Hubbard[2] > > The following people have been involved in previous conversations and would be key to > the face to face discussion. > > John Hubbard > Jan Kara > Dave Chinner > Michal Hocko > Dan Williams > Matthew Wilcox > Jason Gunthorpe > > Thank you, > Ira Weiny > > [1] https://linuxplumbersconf.org/event/2/contributions/126/attachments/136/168/LPC_2018_gup_dma.pdf > [2] https://lkml.org/lkml/2019/2/4/7 >