Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752467AbdCPUno (ORCPT ); Thu, 16 Mar 2017 16:43:44 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:48394 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751663AbdCPUnn (ORCPT ); Thu, 16 Mar 2017 16:43:43 -0400 Date: Thu, 16 Mar 2017 13:43:21 -0700 From: Andrew Morton To: =?ISO-8859-1?Q?J=E9r=F4me?= Glisse Cc: , linux-mm@kvack.org, John Hubbard , Naoya Horiguchi , David Nellans Subject: Re: [HMM 00/16] HMM (Heterogeneous Memory Management) v18 Message-Id: <20170316134321.c5cf727c21abf89b7e6708a2@linux-foundation.org> In-Reply-To: <1489680335-6594-1-git-send-email-jglisse@redhat.com> References: <1489680335-6594-1-git-send-email-jglisse@redhat.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1722 Lines: 39 On Thu, 16 Mar 2017 12:05:19 -0400 J__r__me Glisse wrote: > Cliff note: "Cliff's notes" isn't appropriate for a large feature such as this. Where's the long-form description? One which permits readers to fully understand the requirements, design, alternative designs, the implementation, the interface(s), etc? Have you ever spoken about HMM at a conference? If so, the supporting presentation documents might help here. That's the level of detail which should be presented here. > HMM offers 2 things (each standing on its own). First > it allows to use device memory transparently inside any process > without any modifications to process program code. Well. What is "device memory"? That's very vague. What are the characteristics of this memory? Why is it a requirement that userspace code be unaltered? What are the security implications - does the process need particular permissions to access this memory? What is the proposed interface to set up this access? > Second it allows to mirror process address space on a device. Why? Why is this a requirement, how will it be used, what are the use cases, etc? I spent a bit of time trying to locate a decent writeup of this feature but wasn't able to locate one. I'm not seeing a Documentation/ update in this patchset. Perhaps if you were to sit down and write a detailed Documentation/vm/hmm.txt then that would be a good starting point. This stuff is important - it's not really feasible to perform a decent review of this proposal unless the reviewer has access to this high-level conceptual stuff. So I'll take a look at merging this code as-is for testing purposes but I won't be attempting to review it at this stage.