From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934020AbcCPAVH (ORCPT ); Tue, 15 Mar 2016 20:21:07 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:47888 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932475AbcCPAVF (ORCPT ); Tue, 15 Mar 2016 20:21:05 -0400 Subject: Re: [PATCH 0/4] Remove un-needed 'major' registration when alloc_disk(0) is used. To: NeilBrown , Ross Zwisler References: <20160309215702.20904.61407.stgit@noble> <20160314225017.GC19926@linux.intel.com> <878u1jgzgi.fsf@notabene.neil.brown.name> CC: Keith Busch , Maxim Levitsky , Vishal Verma , Dan Williams , , , From: Jens Axboe Message-ID: <56E8A6BF.7060304@fb.com> Date: Tue, 15 Mar 2016 17:20:15 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <878u1jgzgi.fsf@notabene.neil.brown.name> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.54.13] X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-03-16_01:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/15/2016 03:15 PM, NeilBrown wrote: > On Tue, Mar 15 2016, Ross Zwisler wrote: > >> On Thu, Mar 10, 2016 at 08:59:28AM +1100, NeilBrown wrote: >>> When alloc_disk(0) is used, the ->major number is ignored and >>> irrelevant. Yet several drivers register a major number anyway. >>> >>> This series of patches removes the pointless registrations. The pmem >>> driver also does this, but a patch has already been sent for that >>> driver. >>> >>> Note that I am not in a position to test these beyond simple compile >>> testing. >>> >>> Thanks, >>> NeilBrown >>> >>> >>> --- >>> >>> NeilBrown (4): >>> nvdimm/blk: don't allocate unused major device number >>> nvdimm/btt: don't allocate unused major device number >>> memstick: don't allocate unused major for ms_block >>> NVMe: don't allocate unused nvme_major >>> >>> >>> drivers/memstick/core/ms_block.c | 17 ++--------------- >>> drivers/nvdimm/blk.c | 18 +----------------- >>> drivers/nvdimm/btt.c | 19 ++----------------- >>> drivers/nvme/host/core.c | 16 +--------------- >>> 4 files changed, 6 insertions(+), 64 deletions(-) >> >> There are several other drivers that allocate a major, but then use it for >> some small number of minors (1 for null_blk.c and 16 for virtio_blk.c). They >> both have GENHD_FL_EXT_DEVT set, so I think what happens is that after we >> exhaust the allocated minors they hop over to having BLOCK_EXT_MAJOR as a >> major and a dynamically assigned minor. > > null_blk looks like it would be safe to convert - it is just used for > testing. Jens Axboe would probably know for sure. > > virtio_blk is a much older and there may will be code which has some > sort of expectations about minor numbers. I think it would not be worth > the risks to change it. Agree on both - null_blk can be trivially converted, and I too would be worried about virt_blkio changes breaking existing assumptions. -- Jens Axboe