From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751248AbdJWFSt convert rfc822-to-8bit (ORCPT ); Mon, 23 Oct 2017 01:18:49 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:38898 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750850AbdJWFSq (ORCPT ); Mon, 23 Oct 2017 01:18:46 -0400 Date: Mon, 23 Oct 2017 07:18:35 +0200 From: Martin Schwidefsky To: Christoph Hellwig Cc: Dan Williams , Andrew Morton , Jan Kara , "linux-nvdimm@lists.01.org" , Benjamin Herrenschmidt , Heiko Carstens , "linux-kernel@vger.kernel.org" , linux-xfs@vger.kernel.org, Linux MM , Jeff Moyer , Paul Mackerras , Michael Ellerman , linux-fsdevel , Ross Zwisler , Gerald Schaefer Subject: Re: [PATCH v3 02/13] dax: require 'struct page' for filesystem dax In-Reply-To: <20171020162933.GA26320@lst.de> References: <150846713528.24336.4459262264611579791.stgit@dwillia2-desk3.amr.corp.intel.com> <150846714747.24336.14704246566580871364.stgit@dwillia2-desk3.amr.corp.intel.com> <20171020075735.GA14378@lst.de> <20171020162933.GA26320@lst.de> X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT X-TM-AS-GCONF: 00 x-cbid: 17102305-0008-0000-0000-000004A2C978 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17102305-0009-0000-0000-00001E352D10 Message-Id: <20171023071835.67ee5210@mschwideX1> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-23_02:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1710230076 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 20 Oct 2017 18:29:33 +0200 Christoph Hellwig wrote: > On Fri, Oct 20, 2017 at 08:23:02AM -0700, Dan Williams wrote: > > Yes, however it seems these drivers / platforms have been living with > > the lack of struct page for a long time. So they either don't use DAX, > > or they have a constrained use case that never triggers > > get_user_pages(). If it is the latter then they could introduce a new > > configuration option that bypasses the pfn_t_devmap() check in > > bdev_dax_supported() and fix up the get_user_pages() paths to fail. > > So, I'd like to understand how these drivers have been using DAX > > support without struct page to see if we need a workaround or we can > > go ahead delete this support. If the usage is limited to > > execute-in-place perhaps we can do a constrained ->direct_access() for > > just that case. > > For axonram I doubt anyone is using it any more - it was a very for > the IBM Cell blades, which were produceѕ in a rather limited number. > And Cell basically seems to be dead as far as I can tell. > > For S/390 Martin might be able to help out what the status of xpram > in general and DAX support in particular is. The goes back to the time where DAX was called XIP. The initial design point has been *not* to have struct pages for a large read-only memory area. There is a block device driver for z/VM that maps a DCSS segment somewhere in memore (no struct page!) with e.g. the complete /usr filesystem. The xpram driver is a different beast and has nothing to do with XIP/DAX. Now, if any there are very few users of the dcssblk driver out there. The idea to save a few megabyte for /usr never really took of. We have to look at our get_user_pages() implementation to see how hard it would be to make it fail if the target address is for an area without struct pages. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin.