From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751755AbdJDV3O (ORCPT ); Wed, 4 Oct 2017 17:29:14 -0400 Received: from mail-qt0-f178.google.com ([209.85.216.178]:47575 "EHLO mail-qt0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751197AbdJDV3M (ORCPT ); Wed, 4 Oct 2017 17:29:12 -0400 X-Google-Smtp-Source: AOwi7QDfnjuE6doM4spYRkekKJcEfZAi7bHt4nW8ve8qbjfOic4kLXgN7aJe6AHsO1f+SRP+dbjKew== Subject: Re: [RFC] mmap(MAP_CONTIG) To: Mike Kravetz , Michal Nazarewicz , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org Cc: Marek Szyprowski , "Aneesh Kumar K.V" , Joonsoo Kim , Guy Shattah , Christoph Lameter References: <21f1ec96-2822-1189-1c95-79a2bb491571@oracle.com> From: Laura Abbott Message-ID: <09210624-fb3a-4dc9-5720-49714dbef0f7@redhat.com> Date: Wed, 4 Oct 2017 14:29:08 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/04/2017 10:08 AM, Mike Kravetz wrote: > On 10/04/2017 04:54 AM, Michal Nazarewicz wrote: >> On Tue, Oct 03 2017, Mike Kravetz wrote: >>> At Plumbers this year, Guy Shattah and Christoph Lameter gave a presentation >>> titled 'User space contiguous memory allocation for DMA' [1]. The slides >>> point out the performance benefits of devices that can take advantage of >>> larger physically contiguous areas. >> >> Issue I have is that kind of memory needed may depend on a device. Some >> may require contiguous blocks. Some may support scatter-gather. Some >> may be behind IO-MMU and not care either way. >> >> Furthermore, I feel déjà vu. Wasn’t dmabuf supposed to address this >> issue? > > Thanks Michal, > > I was unaware of dmabuf and am just now looking at capabilities. The > question is whether or not the IB driver writers requesting mmap(MAP_CONTIG) > functionality could make use of dmabuf. That is out of my are of expertise, > so I will let them reply. > I don't think dmabuf as it exists today would help anything here. It's designed to share buffers via fd but you still need some place/driver to actually get the allocation and then export it since there isn't a single interface for allocations. You could convert drivers to take a dma_buf fd if there were appropriate buffers available though. Thanks, Laura