From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f182.google.com (mail-pf0-f182.google.com [209.85.192.182]) by kanga.kvack.org (Postfix) with ESMTP id E68506B0005 for ; Thu, 17 Mar 2016 11:23:43 -0400 (EDT) Received: by mail-pf0-f182.google.com with SMTP id n5so125034029pfn.2 for ; Thu, 17 Mar 2016 08:23:43 -0700 (PDT) Received: from emea01-am1-obe.outbound.protection.outlook.com (mail-am1on0068.outbound.protection.outlook.com. [157.56.112.68]) by mx.google.com with ESMTPS id ua9si2530958pab.25.2016.03.17.08.18.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 17 Mar 2016 08:18:20 -0700 (PDT) Subject: Re: [PATCH RFC 1/1] Add support for ZONE_DEVICE IO memory with struct pages. References: <1457979277-26791-1-git-send-email-stephen.bates@pmcs.com> <20160314212344.GC23727@linux.intel.com> <20160314215708.GA7282@obsidianresearch.com> From: Haggai Eran Message-ID: <56EACAB3.5070301@mellanox.com> Date: Thu, 17 Mar 2016 17:18:11 +0200 MIME-Version: 1.0 In-Reply-To: <20160314215708.GA7282@obsidianresearch.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Jason Gunthorpe , Matthew Wilcox Cc: Stephen Bates , linux-mm@kvack.org, linux-rdma@vger.kernel.org, linux-nvdimm@ml01.01.org, javier@cnexlabs.com, sagig@mellanox.com, leonro@mellanox.com, artemyko@mellanox.com, hch@infradead.org On 3/14/2016 11:57 PM, Jason Gunthorpe wrote: > The other issue is that the fencing mechanism RDMA uses to create > ordering with system memory is not good enough to fence peer-peer > transactions in the general case. It is only possibly good enough if > all the transactions run through the root complex. Are you sure this is a problem? I'm not sure it is clear in the PCIe specs, but I thought that for transactions that are not relaxed-ordered and don't use ID-based ordering, a PCIe switch must prevent reads and writes from passing writes. I assume this is true even when the requestor ID is different because IDO relaxes these constraints specifically for transactions coming from different requestor IDs. Regards, Haggai -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org