From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751449AbdKUXFF (ORCPT ); Tue, 21 Nov 2017 18:05:05 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:38882 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751306AbdKUXFE (ORCPT ); Tue, 21 Nov 2017 18:05:04 -0500 Date: Tue, 21 Nov 2017 15:05:01 -0800 From: Andrew Morton To: Dan Williams Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Christoph Hellwig , stable@vger.kernel.org, linux-nvdimm@lists.01.org Subject: Re: [PATCH v2 1/4] mm: introduce get_user_pages_longterm Message-Id: <20171121150501.d4d811a66444cb5c9cb85bf2@linux-foundation.org> In-Reply-To: <151068939435.7446.13560129395419350737.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151068938905.7446.12333914805308312313.stgit@dwillia2-desk3.amr.corp.intel.com> <151068939435.7446.13560129395419350737.stgit@dwillia2-desk3.amr.corp.intel.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 On Tue, 14 Nov 2017 11:56:34 -0800 Dan Williams wrote: > Until there is a solution to the dma-to-dax vs truncate problem it is > not safe to allow long standing memory registrations against > filesytem-dax vmas. Device-dax vmas do not have this problem and are > explicitly allowed. > > This is temporary until a "memory registration with layout-lease" > mechanism can be implemented for the affected sub-systems (RDMA and > V4L2). Sounds like that will be unpleasant. Do we really need it to be that complex? Can we get away with simply failing the get_user_pages() request? Or are there significant usecases for RDMA and V4L to play with DAX memory?