From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ot0-f197.google.com (mail-ot0-f197.google.com [74.125.82.197]) by kanga.kvack.org (Postfix) with ESMTP id C20616B0038 for ; Tue, 21 Nov 2017 18:26:27 -0500 (EST) Received: by mail-ot0-f197.google.com with SMTP id f28so7660638otd.12 for ; Tue, 21 Nov 2017 15:26:27 -0800 (PST) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id w79sor4889053oiw.296.2017.11.21.15.26.26 for (Google Transport Security); Tue, 21 Nov 2017 15:26:26 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20171121150501.d4d811a66444cb5c9cb85bf2@linux-foundation.org> References: <151068938905.7446.12333914805308312313.stgit@dwillia2-desk3.amr.corp.intel.com> <151068939435.7446.13560129395419350737.stgit@dwillia2-desk3.amr.corp.intel.com> <20171121150501.d4d811a66444cb5c9cb85bf2@linux-foundation.org> From: Dan Williams Date: Tue, 21 Nov 2017 15:26:26 -0800 Message-ID: Subject: Re: [PATCH v2 1/4] mm: introduce get_user_pages_longterm Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Linux MM , "linux-kernel@vger.kernel.org" , Christoph Hellwig , "stable@vger.kernel.org" , "linux-nvdimm@lists.01.org" On Tue, Nov 21, 2017 at 3:05 PM, Andrew Morton wrote: > > 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? V4L plus DAX is indeed dubious, but RDMA to persistent memory is something the RDMA community is interested in supporting [1]. [1]: http://www.snia.org/sites/default/files/SDC15_presentations/persistant_mem/ChetDouglas_RDMA_with_PM.pdf -- 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