From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764695AbdEZMZT (ORCPT ); Fri, 26 May 2017 08:25:19 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:45802 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753276AbdEZMZR (ORCPT ); Fri, 26 May 2017 08:25:17 -0400 Date: Fri, 26 May 2017 14:25:09 +0200 From: Heiko Carstens To: Michal Hocko Cc: Gerald Schaefer , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [-next] memory hotplug regression References: <20170524082022.GC5427@osiris> <20170524083956.GC14733@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170524083956.GC14733@dhcp22.suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) X-TM-AS-GCONF: 00 x-cbid: 17052612-0008-0000-0000-000004559510 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17052612-0009-0000-0000-00001DD45EAD Message-Id: <20170526122509.GB14849@osiris> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-05-26_08:,, 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=8.0.1-1703280000 definitions=main-1705260227 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 24, 2017 at 10:39:57AM +0200, Michal Hocko wrote: > On Wed 24-05-17 10:20:22, Heiko Carstens wrote: > > Having the ZONE_MOVABLE default was actually the only point why s390's > > arch_add_memory() was rather complex compared to other architectures. > > > > We always had this behaviour, since we always wanted to be able to offline > > memory after it was brought online. Given that back then "online_movable" > > did not exist, the initial s390 memory hotplug support simply added all > > additional memory to ZONE_MOVABLE. > > > > Keeping the default the same would be quite important. > > Hmm, that is really unfortunate because I would _really_ like to get rid > of the previous semantic which was really awkward. The whole point of > the rework is to get rid of the nasty zone shifting. > > Is it an option to use `online_movable' rather than `online' in your setup? > Btw. my long term plan is to remove the zone range constrains altogether > so you could online each memblock to the type you want. Would that be > sufficient for you in general? Why is it a problem to change the default for 'online'? As far as I can see that doesn't have too much to do with the order of zones, no? By the way: we played around a bit with the changes wrt memory hotplug. There are a two odd things: 1) With the new code I can generate overlapping zones for ZONE_DMA and ZONE_NORMAL: --- new code: DMA [mem 0x0000000000000000-0x000000007fffffff] Normal [mem 0x0000000080000000-0x000000017fffffff] # cat /sys/devices/system/memory/block_size_bytes 10000000 # cat /sys/devices/system/memory/memory5/valid_zones DMA # echo 0 > /sys/devices/system/memory/memory5/online # cat /sys/devices/system/memory/memory5/valid_zones Normal # echo 1 > /sys/devices/system/memory/memory5/online Normal # cat /proc/zoneinfo Node 0, zone DMA spanned 524288 <----- present 458752 managed 455078 start_pfn: 0 <----- Node 0, zone Normal spanned 720896 present 589824 managed 571648 start_pfn: 327680 <----- So ZONE_DMA ends within ZONE_NORMAL. This shouldn't be possible, unless this restriction is gone? --- old code: # echo 0 > /sys/devices/system/memory/memory5/online # cat /sys/devices/system/memory/memory5/valid_zones DMA # echo online_movable > /sys/devices/system/memory/memory5/state -bash: echo: write error: Invalid argument # echo online_kernel > /sys/devices/system/memory/memory5/state -bash: echo: write error: Invalid argument # echo online > /sys/devices/system/memory/memory5/state # cat /sys/devices/system/memory/memory5/valid_zones DMA 2) Another oddity is that after a memory block was brought online it's association to ZONE_NORMAL or ZONE_MOVABLE seems to be fixed. Even if it is brought offline afterwards: # cat /sys/devices/system/memory/memory16/valid_zones Normal Movable # echo online_movable > /sys/devices/system/memory/memory16/state # echo offline > /sys/devices/system/memory/memory16/state # cat /sys/devices/system/memory/memory16/valid_zones Movable <---- should be "Normal Movable" I assume this happens because start_pfn and spanned pages of the zones aren't updated if a memory block at the beginning or end of a zone is brought offline.