From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f198.google.com (mail-io0-f198.google.com [209.85.223.198]) by kanga.kvack.org (Postfix) with ESMTP id 207E56B02E1 for ; Mon, 1 May 2017 21:29:19 -0400 (EDT) Received: by mail-io0-f198.google.com with SMTP id 194so66899757iof.21 for ; Mon, 01 May 2017 18:29:19 -0700 (PDT) Received: from mail-pg0-x242.google.com (mail-pg0-x242.google.com. [2607:f8b0:400e:c05::242]) by mx.google.com with ESMTPS id 126si386338ity.6.2017.05.01.18.29.17 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 01 May 2017 18:29:18 -0700 (PDT) Received: by mail-pg0-x242.google.com with SMTP id t7so18473658pgt.1 for ; Mon, 01 May 2017 18:29:17 -0700 (PDT) Message-ID: <1493688548.15044.1.camel@gmail.com> Subject: Re: [RFC 0/4] RFC - Coherent Device Memory (Not for inclusion) From: Balbir Singh Date: Tue, 02 May 2017 11:29:08 +1000 In-Reply-To: <91272c14-81df-9529-f0ae-6abb17a694ea@nvidia.com> References: <20170419075242.29929-1-bsingharora@gmail.com> <91272c14-81df-9529-f0ae-6abb17a694ea@nvidia.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: John Hubbard , linux-mm@kvack.org, akpm@linux-foundation.org Cc: khandual@linux.vnet.ibm.com, benh@kernel.crashing.org, aneesh.kumar@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com, srikar@linux.vnet.ibm.com, haren@linux.vnet.ibm.com, jglisse@redhat.com, mgorman@techsingularity.net, mhocko@kernel.org, arbab@linux.vnet.ibm.com, vbabka@suse.cz, cl@linux.com On Mon, 2017-05-01 at 13:41 -0700, John Hubbard wrote: > On 04/19/2017 12:52 AM, Balbir Singh wrote: > > This is a request for comments on the discussed approaches > > for coherent memory at mm-summit (some of the details are at > > https://lwn.net/Articles/717601/). The latest posted patch > > series is at https://lwn.net/Articles/713035/. I am reposting > > this as RFC, Michal Hocko suggested using HMM for CDM, but > > we believe there are stronger reasons to use the NUMA approach. > > The earlier patches for Coherent Device memory were implemented > > and designed by Anshuman Khandual. > > > > Hi Balbir, > > Although I think everyone agrees that in the [very] long term, these > hardware-coherent nodes probably want to be NUMA nodes, in order to decide what to > code up over the next few years, we need to get a clear idea of what has to be done > for each possible approach. > > Here, the CDM discussion is falling just a bit short, because it does not yet > include the whole story of what we would need to do. Earlier threads pointed this > out: the idea started as a large patchset RFC, but then, "for ease of review", it > got turned into a smaller RFC, which loses too much context. Hi, John I thought I explained the context, but I'll try again. I see the whole solution as a composite of the following primitives: 1. Enable hotplug of CDM nodes 2. Isolation of CDM memory 3. Migration to/from CDM memory 4. Performance enhancements for migration The RFC here is for (2) above. (3) is handled by HMM and (4) is being discussed in the community. I think the larger goals are same as HMM, except that we don't need unaddressable memory, since the memory is cache coherent. > > So, I'd suggest putting together something more complete, so that it can be fairly > compared against the HMM-for-hardware-coherent-nodes approach. > Since I intend to reuse bits of HMM, I am not sure if I want to repost those patches as a part of my RFC. I hope my answers make sense, the goal is to reuse as much of what is available. From a user perspective 1. We see no new interface being added in either case, the programming model would differ though 2. We expect the programming model to be abstracted behind a user space framework, potentially like CUDA or CXL > > > Jerome posted HMM-CDM at https://lwn.net/Articles/713035/. > > The patches do a great deal to enable CDM with HMM, but we > > still believe that HMM with CDM is not a natural way to > > represent coherent device memory and the mm will need > > to be audited and enhanced for it to even work. > > That is also true for the CDM approach. Specifically, in order for this to be of any > use to device drivers, we'll need the following: > Since Reza answered these questions, I'll skip them in this email Thanks for the review! Balbir Singh -- 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