Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1172682AbdDYHI4 (ORCPT ); Tue, 25 Apr 2017 03:08:56 -0400 Received: from edison.jonmasters.org ([173.255.233.168]:60767 "EHLO edison.jonmasters.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1170608AbdDYHIr (ORCPT ); Tue, 25 Apr 2017 03:08:47 -0400 To: John Hubbard , Dan Williams , Jerome Glisse References: <20170422033037.3028-1-jglisse@redhat.com> <20170422033037.3028-4-jglisse@redhat.com> <20170422181151.GA2360@redhat.com> Cc: Andrew Morton , "linux-kernel@vger.kernel.org" , Linux MM , Naoya Horiguchi , David Nellans , Ross Zwisler From: Jon Masters Organization: World Organi{s,z}ation Of Broken Dreams Message-ID: Date: Tue, 25 Apr 2017 03:08:43 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 74.92.29.237 X-SA-Exim-Mail-From: jcm@jonmasters.org Subject: Re: [HMM 03/15] mm/unaddressable-memory: new type of ZONE_DEVICE for unaddressable memory X-SA-Exim-Version: 4.2.1 (built Sun, 08 Nov 2009 07:31:22 +0000) X-SA-Exim-Scanned: Yes (on edison.jonmasters.org) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 912 Lines: 17 On 04/23/2017 08:39 PM, John Hubbard wrote: > Actually, MEMORY_DEVICE_PRIVATE / _PUBLIC seems like a good choice to > me, because the memory may not remain CPU-unaddressable in the future. > By that, I mean that I know of at least one company (ours) that is > working on products that will support hardware-based memory coherence > (and access counters to go along with that). If someone were to enable > HMM on such a system, then the device memory would be, in fact, directly > addressable by a CPU--thus exactly contradicting the "unaddressable" name. I'm expecting similar with CCIX-like coherently attached accelerators running within FPGAs and as discrete devices as well. Everyone and their dog is working on hardware based coherence as a programming convenience and so the notion of ZONE_DEVICE as it stood is going to rapidly evolve over the next 18 months, maybe less. Short term anyway. Jon.