From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752670AbdB1NgY (ORCPT ); Tue, 28 Feb 2017 08:36:24 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:51135 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752539AbdB1NgT (ORCPT ); Tue, 28 Feb 2017 08:36:19 -0500 Date: Tue, 28 Feb 2017 11:21:05 +0100 From: Heiko Carstens To: Michal Hocko Cc: Vitaly Kuznetsov , linux-mm@kvack.org, Andrew Morton , Greg KH , "K. Y. Srinivasan" , David Rientjes , Daniel Kiper , linux-api@vger.kernel.org, LKML , linux-s390@vger.kernel.org, xen-devel@lists.xenproject.org, linux-acpi@vger.kernel.org Subject: Re: [RFC PATCH] mm, hotplug: get rid of auto_online_blocks References: <20170227092817.23571-1-mhocko@kernel.org> <87lgssvtni.fsf@vitty.brq.redhat.com> <20170227112510.GA4129@osiris> <20170227154304.GK26504@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170227154304.GK26504@dhcp22.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 17022810-0028-0000-0000-000002B33F32 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17022810-0029-0000-0000-000022875897 Message-Id: <20170228102105.GA13872@osiris> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-02-28_07:,, 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=8.0.1-1612050000 definitions=main-1702280096 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 27, 2017 at 04:43:04PM +0100, Michal Hocko wrote: > On Mon 27-02-17 12:25:10, Heiko Carstens wrote: > > On Mon, Feb 27, 2017 at 11:02:09AM +0100, Vitaly Kuznetsov wrote: > > > A couple of other thoughts: > > > 1) Having all newly added memory online ASAP is probably what people > > > want for all virtual machines. > > > > This is not true for s390. On s390 we have "standby" memory that a guest > > sees and potentially may use if it sets it online. Every guest that sets > > memory offline contributes to the hypervisor's standby memory pool, while > > onlining standby memory takes memory away from the standby pool. > > > > The use-case is that a system administrator in advance knows the maximum > > size a guest will ever have and also defines how much memory should be used > > at boot time. The difference is standby memory. > > > > Auto-onlining of standby memory is the last thing we want. > > > > > Unfortunately, we have additional complexity with memory zones > > > (ZONE_NORMAL, ZONE_MOVABLE) and in some cases manual intervention is > > > required. Especially, when further unplug is expected. > > > > This also is a reason why auto-onlining doesn't seem be the best way. > > Can you imagine any situation when somebody actually might want to have > this knob enabled? From what I understand it doesn't seem to be the > case. I can only speak for s390, and at least here I think auto-online is always wrong, especially if you consider the added complexity that you may want to online memory sometimes to ZONE_NORMAL and sometimes to ZONE_MOVABLE.