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,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 5A5CFC43381 for ; Fri, 15 Feb 2019 23:38:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 27B3D222DF for ; Fri, 15 Feb 2019 23:38:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389120AbfBOXig (ORCPT ); Fri, 15 Feb 2019 18:38:36 -0500 Received: from mga04.intel.com ([192.55.52.120]:52883 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388691AbfBOXig (ORCPT ); Fri, 15 Feb 2019 18:38:36 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 15 Feb 2019 15:38:35 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,374,1544515200"; d="scan'208";a="134717010" Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by orsmga002.jf.intel.com with ESMTP; 15 Feb 2019 15:38:34 -0800 Date: Fri, 15 Feb 2019 15:38:29 -0800 From: Ira Weiny To: Jason Gunthorpe Cc: Christopher Lameter , Matthew Wilcox , Dave Chinner , Jerome Glisse , Dan Williams , Jan Kara , Doug Ledford , lsf-pc@lists.linux-foundation.org, linux-rdma , Linux MM , Linux Kernel Mailing List , John Hubbard , Michal Hocko Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA Message-ID: <20190215233828.GB30818@iweiny-DESK2.sc.intel.com> References: <20190211180654.GB24692@ziepe.ca> <20190214202622.GB3420@redhat.com> <20190214205049.GC12668@bombadil.infradead.org> <20190214213922.GD3420@redhat.com> <20190215011921.GS20493@dastard> <01000168f1d25e3a-2857236c-a7cc-44b8-a5f3-f51c2cfe6ce4-000000@email.amazonses.com> <20190215180852.GJ12668@bombadil.infradead.org> <01000168f26d9e0c-aef3255a-5059-4657-b241-dae66663bbea-000000@email.amazonses.com> <20190215220031.GB8001@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190215220031.GB8001@ziepe.ca> 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 On Fri, Feb 15, 2019 at 03:00:31PM -0700, Jason Gunthorpe wrote: > On Fri, Feb 15, 2019 at 06:31:36PM +0000, Christopher Lameter wrote: > > On Fri, 15 Feb 2019, Matthew Wilcox wrote: > > > > > > Since RDMA is something similar: Can we say that a file that is used for > > > > RDMA should not use the page cache? > > > > > > That makes no sense. The page cache is the standard synchronisation point > > > for filesystems and processes. The only problems come in for the things > > > which bypass the page cache like O_DIRECT and DAX. > > > > It makes a lot of sense since the filesystems play COW etc games with the > > pages and RDMA is very much like O_DIRECT in that the pages are modified > > directly under I/O. It also bypasses the page cache in case you have > > not noticed yet. > > It is quite different, O_DIRECT modifies the physical blocks on the > storage, bypassing the memory copy. > Really? I thought O_DIRECT allowed the block drivers to write to/from user space buffers. But the _storage_ was still under the control of the block drivers? > > RDMA modifies the memory copy. > > pages are necessary to do RDMA, and those pages have to be flushed to > disk.. So I'm not seeing how it can be disconnected from the page > cache? I don't disagree with this. Ira > > Jason